Syntax and semantics for adaptive loop filter and sample adaptive offset

ABSTRACT

The present invention provides an improved video encoding and decoding method, which maintains the advantages of LCU-based filter parameter signaling as compared to frame-based filter parameter signaling, but considerably reduces signaling overhead. Therefore, signaling syntax is modified by grouping LCUs (Largest Coding Units) together for signaling employing a mapping function. Consequently, filter parameters no longer need to be signaled for each single LCU, but for a group of several LCUs. The syntax structure of the invention avoids redundancies present in the state of the art as far as possible and thus increases the information content of the syntax elements. At the decoder side, the mapping function is applied to infer information about the filter parameters to be applied to a current LCU from information encoded in different syntax structures.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/EP2013/056401, filed Mar. 26, 2013, which claims the benefit of U.S.Provisional Patent Application No. 61/617,915, filed Mar. 30, 2012. Theentire disclosures of the above-identified applications, including thespecifications, drawings and claims are incorporated herein by referencein their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of video image coding anddecoding. In particular, the present invention relates toencoding/decoding employing filters with variable filter parameters.

2. Description of the Related Art

At present, the majority of standardized video coding algorithms arebased on hybrid video coding. Hybrid video coding methods typicallycombine several different lossless and lossy compression schemes inorder to achieve the desired compression gain. Hybrid video coding isalso the basis for ITU-T standards (H.26x standards such as H.261,H.263) as well as ISO/IEC standards (MPEG-X standards such as MPEG-1,MPEG-2, and MPEG-4). The most recent and advanced video coding standardis currently the standard denoted as H.264/MPEG-4 advanced video coding(AVC) which is a result of standardization efforts by joint video team(JVT), a joint team of ITU-T and ISO/IEC MPEG groups. This codec isbeing further developed by Joint Collaborative Team on Video Coding(JCT-VC) under a name High-Efficiency Video Coding (HEVC), aiming, inparticular at improvements of efficiency regarding the high-resolutionvideo coding.

A video signal input to an encoder is a sequence of images calledframes, each frame being a two-dimensional matrix of pixels. All theabove-mentioned standards based on hybrid video coding includesubdividing each individual video frame into smaller blocks consistingof a plurality of pixels. The size of the blocks may vary, for instance,in accordance with the content of the image. The way of coding may betypically varied on a per block basis. The largest possible size forsuch a block, for instance in HEVC, is 64×64 pixels. It is then calledthe largest coding unit (LCU). In H.264/MPEG-4 AVC, a macroblock(usually denoting a block of 16×16 pixels) was the basic image element,for which the encoding is performed, with a possibility to furtherdivide it in smaller subblocks to which some of the coding/decodingsteps were applied.

Typically, the encoding steps of a hybrid video coding include a spatialand/or a temporal prediction. Accordingly, each block to be encoded isfirst predicted using either the blocks in its spatial neighborhood orblocks from its temporal neighborhood, i.e. from previously encodedvideo frames. A block of differences between the block to be encoded andits prediction, also called block of prediction residuals, is thencalculated. Another encoding step is a transformation of a block ofresiduals from the spatial (pixel) domain into a frequency domain. Thetransformation aims at reducing the correlation of the input block.Further encoding step is quantization of the transform coefficients. Inthis step the actual lossy (irreversible) compression takes place.Usually, the compressed transform coefficient values are furthercompacted (losslessly compressed) by means of an entropy coding. Inaddition, side information necessary for reconstruction of the encodedvideo signal is encoded and provided together with the encoded videosignal. This is for example information about the spatial and/ortemporal prediction, amount of quantization, etc.

FIG. 1 is an example of a typical H.264/MPEG-4 AVC and/or HEVC videoencoder 100. A subtractor 105 first determines differences e between acurrent block to be encoded of an input video image (input signal s) anda corresponding prediction block ŝ, which is used as a prediction of thecurrent block to be encoded. The prediction signal may be obtained by atemporal or by a spatial prediction 180. The type of prediction can bevaried on a per frame basis or on a per block basis. Blocks and/orframes predicted using temporal prediction are called “inter”-encodedand blocks and/or frames predicted using spatial prediction are called“intra”-encoded. Prediction signal using temporal prediction is derivedfrom the previously encoded images, which are stored in a memory. Theprediction signal using spatial prediction is derived from the values ofboundary pixels in the neighboring blocks, which have been previouslyencoded, decoded, and stored in the memory. The difference e between theinput signal and the prediction signal, denoted prediction error orresidual, is transformed 110 resulting in coefficients, which arequantized 120. Entropy encoder 190 is then applied to the quantizedcoefficients in order to further reduce the amount of data to be storedand/or transmitted in a lossless way. This is mainly achieved byapplying a code with code words of variable length wherein the length ofa code word is chosen based on the probability of its occurrence.

Within the video encoder 100, a decoding unit is incorporated forobtaining a decoded (reconstructed) video signal s′. In compliance withthe encoding steps, the decoding steps include dequantization andinverse transformation 130. The so obtained prediction error signal e′differs from the original prediction error signal due to thequantization error, called also quantization noise. A reconstructedimage signal s′ is then obtained by adding 140 the decoded predictionerror signal e′ to the prediction signal ŝ. In order to maintain thecompatibility between the encoder side and the decoder side, theprediction signal ŝ is obtained based on the encoded and subsequentlydecoded video signal which is known at both sides the encoder and thedecoder.

Due to the quantization, quantization noise is superposed to thereconstructed video signal. Due to the block-wise coding, the superposednoise often has blocking characteristics, which result, in particularfor strong quantization, in visible block boundaries in the decodedimage. Such blocking artifacts have a negative effect upon human visualperception. In order to reduce these artifacts, a deblocking filter 150is applied to every reconstructed image block. The deblocking filter isapplied to the reconstructed signal s′. For instance, the deblockingfilter of H.264/MPEG-4 AVC has the capability of local adaptation. Inthe case of a high degree of blocking noise, a strong (narrow-band) lowpass filter is applied, whereas for a low degree of blocking noise, aweaker (broad-band) low pass filter is applied. The strength of the lowpass filter is determined by the prediction signal ŝ and by thequantized prediction error signal e′. Deblocking filter generallysmoothes the block edges leading to an improved subjective quality ofthe decoded images. Moreover, since the filtered part of an image isused for the motion compensated prediction of further images, thefiltering also reduces the prediction errors, and thus enablesimprovement of coding efficiency.

After a deblocking filter, a sample adaptive offset 155 and/or adaptiveloop filter 160 may be applied to the image including the alreadydeblocked signal s″. Whereas the deblocking filter improves thesubjective quality, Sample Adaptive Offset (SAO) and ALF aim atimproving the pixel-wise fidelity (“objective” quality). In particular,SAO adds an offset in accordance with the immediate neighborhood of apixel. The Adaptive Loop Filter (ALF) is used to compensate imagedistortion caused by the compression. Typically, the adaptive loopfilter is a Wiener filter with filter coefficients determined such thatthe mean square error (MSE) between the reconstructed s′ and sourceimages s is minimized. The coefficients of ALF may be calculated andtransmitted on a frame basis. ALF can be applied to the entire frame(image of the video sequence) or to local areas (blocks). An additionalside information indicating which areas are to be filtered may betransmitted (block-based, frame-based or quadtree-based).

In order to be decoded, inter-encoded blocks require also storing thepreviously encoded and subsequently decoded portions of image(s) in thereference frame buffer 170. An inter-encoded block is predicted 180 byemploying motion compensated prediction. First, a best-matching block isfound for the current block within the previously encoded and decodedvideo frames by a motion estimator. The best-matching block then becomesa prediction signal and the relative displacement (motion) between thecurrent block and its best match is then signalized as motion data inthe form of three-dimensional motion vectors within the side informationprovided together with the encoded video data. The three dimensionsconsist of two spatial dimensions and one temporal dimension. In orderto optimize the prediction accuracy, motion vectors may be determinedwith a spatial sub-pixel resolution e.g. half pixel or quarter pixelresolution. A motion vector with spatial sub-pixel resolution may pointto a spatial position within an already decoded frame where no realpixel value is available, i.e. a sub-pixel position. Hence, spatialinterpolation of such pixel values is needed in order to perform motioncompensated prediction. This may be achieved by an interpolation filter(in FIG. 1 integrated within Prediction block 180).

For both, the intra- and the inter-encoding modes, the differences ebetween the current input signal and the prediction signal aretransformed 110 and quantized 120, resulting in the quantizedcoefficients. Generally, an orthogonal transformation such as atwo-dimensional discrete cosine transformation (DCT) or an integerversion thereof is employed since it reduces the correlation of thenatural video images efficiently. After the transformation, lowerfrequency components are usually more important for image quality thenhigh frequency components so that more bits can be spent for coding thelow frequency components than the high frequency components. In theentropy coder, the two-dimensional matrix of quantized coefficients isconverted into a one-dimensional array. Typically, this conversion isperformed by a so-called zig-zag scanning, which starts with theDC-coefficient in the upper left corner of the two-dimensional array andscans the two-dimensional array in a predetermined sequence ending withan AC coefficient in the lower right corner. As the energy is typicallyconcentrated in the left upper part of the two-dimensional matrix ofcoefficients, corresponding to the lower frequencies, the zig-zagscanning results in an array where usually the last values are zero.This allows for efficient encoding using run-length codes as a partof/before the actual entropy coding.

The H.264/MPEG-4 H.264/MPEG-4 AVC as well as HEVC includes twofunctional layers, a Video Coding Layer (VCL) and a Network AbstractionLayer (NAL). The VCL provides the encoding functionality as brieflydescribed above. The NAL encapsulates information elements intostandardized units called NAL units according to their furtherapplication such as transmission over a channel or storing in storage.The information elements are, for instance, the encoded prediction errorsignal or other information necessary for the decoding of the videosignal such as type of prediction, quantization parameter, motionvectors, etc. There are VCL NAL units containing the compressed videodata and the related information, as well as non-VCL units encapsulatingadditional data such as parameter set relating to an entire videosequence, or a Supplemental Enhancement Information (SEI) providingadditional information that can be used to improve the decodingperformance.

FIG. 2 illustrates an example decoder 200 according to the H.264/MPEG-4AVC or HEVC video coding standard. The encoded video signal (inputsignal to the decoder) first passes to entropy decoder 290, whichdecodes the quantized coefficients, the information elements necessaryfor decoding such as motion data, mode of prediction etc. The quantizedcoefficients are inversely scanned in order to obtain a two-dimensionalmatrix, which is then fed to inverse quantization and inversetransformation 230. After inverse quantization and inversetransformation 230, a decoded (quantized) prediction error signal e′ isobtained, which corresponds to the differences obtained by subtractingthe prediction signal from the signal input to the encoder in the caseno quantization noise is introduced and no error occurred.

The prediction signal is obtained from either a temporal or a spatialprediction 280. The decoded information elements usually further includethe information necessary for the prediction such as prediction type inthe case of intra-prediction and motion data in the case of motioncompensated prediction. The quantized prediction error signal in thespatial domain is then added with an adder 240 to the prediction signalobtained either from the motion compensated prediction or intra-frameprediction 280. The reconstructed image s′ may be passed through adeblocking filter 250, sample adaptive offset processing 255, and anadaptive loop filter 260 and the resulting decoded signal is stored inthe memory 270 to be applied for temporal or spatial prediction of thefollowing blocks/images.

The information that is required for correct decoding and reconstructionof a video sequence is usually encoded and transmitted together with thevideo data in the transmitted bit stream. Information is usuallyallocated into video slices and different kinds of parameter sets. Theparticular syntax structures used and respective allocation schemes havea strong influence on coding efficiency as well as on the amount of datatransmitted (network abstraction layer NAL).

Basically, there are two types of SAO and ALF filter estimationprinciples that are applied with standard hybrid coders, such asillustrated in FIG. 1. The first one is called frame-based filterparameter estimation (design). This means that the process of designing(optimizing) filter parameters is performed jointly for all of thepixels of a frame. In other words, in this approach a filter parameterset is designed jointly for all of the Largest Coding Units (LCU) of aframe.

The second type is called LCU-based filter parameter estimation. In thistype, the process of designing filter parameters is performed one by onefor each LCU in a frame. Usually, no look-ahead is allowed (as opposedto the frame-based method), meaning that the LCUs that follow thecurrent LCU in the coding order are assumed to be unavailable to thefilter design process.

Both types of filter estimation have certain advantages and drawbacks.

Frame-based filter estimation is superior to LCU-based estimation withrespect to coding gain due to the joint estimation procedure. However,compared to the LCU-based approach, the frame-based approach createsadditional delay in the encoder and requires additional external memoryaccess. In view of the additional delay introduced by the frame-basedapproach, LCU-based ALF and SAO are more suitable for low-delayapplications. In correspondence with the two different approaches tofilter parameter estimation, two different syntax structures employedfor encoding the filter parameter information have been developed.

A first syntax structure is called the frame-based filter parameter setsyntax structure. This syntax structure is used to represent the filterparameter set that is designed for a whole frame. A frame-based syntaxstructure can be generated for each frame, meaning that the smallestunit is a frame. In accordance therewith, a single set of filterparameters for a filter is designed and transmitted corresponding toeach frame in a sequence.

A second syntax structure is called the LCU-based filter parameter setsyntax structure. The smallest syntax unit is an LCU. A parameter setsyntax structure is generated for each LCU. The LCU-based syntaxstructure supports both frame-based filter parameter estimation andLCU-based filter parameter estimation. In accordance therewith, a filterparameter set for each filter is transmitted (signaled) for each LCU.

Further details regarding said syntax structures have been set forth instandardization documents and will be described in the detaileddescription section with reference to the respective standardizationdocuments.

Both types of syntax structure have advantages and drawbacks that areclosely related to the different types of filter parameter estimationschemes discussed above.

Since frame-based syntax is only applicable to frame-based filterparameter estimation, it creates an additional delay (frame-levelencoding delay). Therefore, frame-based syntax is not suitable forlow-delay applications such as teleconferencing. Further, the enhancedexternal memory access requirements in the encoder represent a drawbackof frame-based syntax structures.

Therefore, the LCU-based syntax has been adopted to replace theframe-based syntax. The LCU-based syntax supports both LCU-based andframe-based filer estimation. Therefore, it is more flexible compared toframe-based parameter set syntax and can achieve lower encoding delays.However, it is a drawback of LCU-based syntax that an LCU parameter unitmust be transmitted (signaled) for each LCU. Therefore, LCU-based syntaxcauses more parameter signaling overhead compared to the frame-basedapproach. Due to the higher level of signaling overhead, the LCU-basedsyntax causes coding loss compared to the frame-based syntax, even inthe case of frame-based estimation. Since the filtering controlparameters need to be signaled for each and every LCU in a frame, thesize of the parameter syntax structure increases with increasing framesize and decreasing LCU size (i.e. increasing number of LCUs per frame).

SUMMARY OF THE INVENTION

The present invention aims to provide an improved coding scheme thatmaintains the flexibility of LCU-based filter parameter set syntax whileallowing a reduced signaling overhead, and corresponding encoding anddecoding methods and apparatuses.

According to a first aspect of the present invention, a video decodingmethod for decoding video that has been encoded by employing at leastone filter with variable filter parameters is provided. The filterparameters are set for groups of Largest Coding Units. The methodcomprises the steps of parsing a first syntax structure for retrievinginformation specifying the number of said groups per picture and parsinga second syntax structure for retrieving information specifying thenumber of Largest Coding Units per picture. The method further comprisesthe step of applying a predetermined mapping function to the informationretrieved from the first and the second syntax structures. Thereby,information specifying the filter parameters to be applied in decoding aparticular Largest Coding Unit of the video is generated.

According to a second aspect of the present invention, a video encodingmethod is provided. The method employs at least one filter havingvariable filter parameters. The filter parameters are determined andencoded adaptively on the basis of groups of plural Largest CodingUnits. The method comprises the steps of generating syntax elementsspecifying the number of said groups per picture and including saidsyntax elements into a syntax structure adapted for defining filterparameters on the basis of single Largest Coding Units in place ofsyntax elements specifying the number of Largest Coding Units perpicture.

According to a third aspect of the present invention, a video decodingapparatus for decoding video that has been encoded by employing at leastone filter with variable filter parameters is provided. The filterparameters are set for groups of Largest Coding Units. The decodingapparatus comprises at least one filter having variable filterparameters. The apparatus further comprises a first parser for parsing afirst syntax structure for retrieving information specifying the numberof said groups per picture and a second parser for parsing a secondsyntax structure for retrieving information specifying the number ofLargest Coding Units per picture. Moreover, the apparatus comprises afilter information generator for applying a predetermined mappingfunction to the information retrieved from the first and the secondsyntax structures, thereby generating information specifying the filterparameters of the at least one filter to be applied in decoding aparticular Largest Coding Unit of the video.

According to a fourth aspect of the present invention, a video encodingapparatus is provided. The video encoding apparatus comprises at leastone filter having variable filter parameters. The filter parameters aredetermined and encoded adaptively on the basis of groups of pluralLargest Coding Units. The apparatus further comprises a unit forgenerating syntax elements specifying the number of said groups perpicture, and a unit for including the syntax elements into a syntaxstructure adapted for defining filter parameters on the basis of singleLargest Coding Units in place of syntax elements specifying the numberof Largest Coding Units per picture.

It is the particular approach of the present invention to determine andsignal filter parameters of variable filters employed in encoding anddecoding of a video on the basis of groups of Largest Coding Units(LCU). Therefore, an LCU-based syntax structure such as APS (adaptationparameter set) generally employed for signaling parameters on a singleLCU basis is modified to replace redundant information about the LCUnumber per picture with information about the number of LCU groups perpicture. A mapping function determines, how the LCUs of a frame aregrouped. At the decoder side, the mapping function is applied, in orderto determine to which LCU group a particular LCU belongs, based oninformation about the number of LCUs and the number LCU groups encodedin different syntax structures such as APS and SPS (Sequence ParameterSet). Thereby, the advantages of LCU-based signaling syntax arepreserved, while the size of the signaling overhead is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated into and form a part of aspecification to illustrate several embodiments of the presentinvention. These drawings, together with the description, serve toexplain the principles of the invention. The drawings are only for thepurpose of illustrating preferred and alternative examples of how theinvention can be made and used, and are not to be construed as limitingthe invention to only the illustrated and described embodiments. Furtherfeatures and advantages will become apparent from the following and moreparticular description of the various embodiments of the invention, asillustrated in the accompanying drawings, in which like referencenumbers refer to like elements and wherein:

FIG. 1 is a block diagram illustrating an example of a video encoder;

FIG. 2 is a block diagram illustrating an example of a video decoder;

FIG. 3 provides a general example for employing LCU-based parametersyntax for Adaptive Loop Filter (ALF) and Sample Adaptive Offset (SAO);

FIG. 4 illustrates RBSP (Rule Byte Sequence Payload) syntax within anadaptation parameter set;

FIG. 5 provides an illustration of sample adaptive offset parametersyntax;

FIG. 6 provides an illustration of adaptive loop filter parametersyntax;

FIG. 7 provides an illustration of additional syntax elements introducedwithin the framework of APS in accordance with the present invention;

FIG. 8 illustrates the adaptation of APS syntax parameters in accordancewith an embodiment of the present invention;

FIG. 9 illustrates an example of sample adaptive offset parameter syntaxin accordance with an embodiment of the present invention;

FIG. 10 provides an illustration of reference relationship within atransmitted encoded bit stream in accordance with an embodiment of thepresent invention;

FIG. 11 is a flow diagram illustrating coding processing in accordancewith an embodiment of the present invention;

FIG. 12 illustrates a process of partitioning a frame into LCUs andregions for signaling filter parameters in accordance with an embodimentof the present invention;

FIG. 13 illustrates a result of generating LCU groups in accordance witha first exemplary mapping function of the present invention;

FIG. 14 illustrates a result of generating LCU groups in accordance witha second exemplary mapping function of the present invention;

FIG. 15 provides an illustration of improved referencing possibilitieson the basis of the present invention;

FIG. 16 shows an overall configuration of a content providing system forimplementing content distribution services.

FIG. 17 shows an overall configuration of a digital broadcasting system.

FIG. 18 shows a block diagram illustrating an example of a configurationof a television.

FIG. 19 shows a block diagram illustrating an example of a configurationof an information reproducing/recording unit that reads and writesinformation from and on a recording medium that is an optical disk.

FIG. 20 shows an example of a configuration of a recording medium thatis an optical disk.

FIG. 21A shows an example of a cellular phone.

FIG. 21B is a block diagram showing an example of a configuration of acellular phone.

FIG. 22 illustrates a structure of multiplexed data.

FIG. 23 schematically shows how each stream is multiplexed inmultiplexed data.

FIG. 24 shows how a video stream is stored in a stream of PES packets inmore detail.

FIG. 25 shows a structure of TS packets and source packets in themultiplexed data.

FIG. 26 shows a data structure of a PMT.

FIG. 27 shows an internal structure of multiplexed data information.

FIG. 28 shows an internal structure of stream attribute information.

FIG. 29 shows steps for identifying video data.

FIG. 30 shows an example of a configuration of an integrated circuit forimplementing the moving picture coding method and the moving picturedecoding method according to each of embodiments.

FIG. 31 shows a configuration for switching between driving frequencies.

FIG. 32 shows steps for identifying video data and switching betweendriving frequencies.

FIG. 33 shows an example of a look-up table in which video datastandards are associated with driving frequencies.

FIG. 34A is a diagram showing an example of a configuration for sharinga module of a signal processing unit.

FIG. 34B is a diagram showing another example of a configuration forsharing a module of the signal processing unit.

DETAILED DESCRIPTION OF THE INVENTION

State of the art hybrid video coders such as those illustrated in FIG. 1apply in-loop Deblocking Filter (DF), Sample Adaptive Offset (SAO) andAdaptive Loop Filter (ALF) processing stages before the reconstructedframe is displayed on the screen or stored at the reference framebuffer. These processes are essentially filtering stages that improvethe objective and/or subjective quality of the frame before displayingon the screen. The DF improves the subjective quality, whereas SAO andALF improve both subjective and objective qualities. The controlparameters associated with SAO and ALF processes are signaled in the bitstream. More specifically, since the operation of the SAO and ALFfilters has an adaptive nature, control parameters are transmitted inthe bit stream so that the decoder can successfully decode the videodata. Control parameters for ALF may include, for instance, a flagindicating whether the ALF is applied on a picture slice or not, filtershape, filter coefficients, etc. Corresponding information may beincluded by the SAO parameters.

ALF and SAO control parameters are usually signaled within the NetworkAbstraction Layer (NAL). In order to group at least some of these data,they may be included within a parameter set called Adaptation ParameterSet (APS). Alternatively, filter parameter signaling is possible insidea picture slice.

Further details regarding filter control parameters and respectivesyntax conventions have been defined in the following prior artreferences (standard documents) that are hereby incorporated byreference in their entirety:

-   [1] JCTVC-F056 version 5, “Sample Adaptive Offset with LCU-based    Syntax”, Torino, July, 2011-   [2] JCTVC-G498 version 3, “CE8: ALF with low latency and reduced    complexity”, Geneva, November, 2011-   [3] JCTVC-H1003 version 21, “WD4: Working Draft 6 of High-Efficiency    Video Coding”, San Jose, February, 2012-   [4] JCTVC-G1103 version 10, “WD5: Working Draft 5 of High-Efficiency    Video Coding”, Geneva, November 2011

As briefly introduced above, frame-based parameter syntax and LCU-basedparameter syntax for ALF and SAO are generally distinguished.

Frame-based parameter syntax is described in prior art document [4].

A general example for a frame-based parameter syntax structure is givenbelow (for the case of ALF):

ALF_parameter_set {  no_filters_per_frame;  for (i=0 ;i<no_filters_per_frame ; i++)     filter_coefficients( ); frame_partition_info( );  //how the transmitted filters are matched toeach region in a frame }

The parameter “frame_partition_info( ) in the last line of said examplerelates to the “quadtree” partitioning of a frame into four, ormoreover, sixteen partitions.

In accordance with frame-based parameter syntax, one ALF_parameter_setis designed and transmitted corresponding to each frame in a sequence.

The general structure of the frame-based parameter syntax structure forSAO corresponds to the illustrated one for ALF. An exemplaryillustration thereof has therefore been omitted.

There are the following problems in the framework of frame-basedparameter set syntax:

Frame-based filter parameter set syntax structure causes frame levelencoding delay in the encoder. Usually, a frame can be divided intomultiple slices in order to reduce the delay between encoding anddecoding (sub-picture level delay). However, when ALF and SAO are turnedon, sub-picture level delay cannot be achieved due to frame-based filterparameter estimation.

Moreover, frame-based filter parameter estimation increases the memoryaccess requirements in the encoder. The frame-based filter estimationprocess can be summarized in three steps:

-   -   1. Read a whole frame from memory in order to compute        statistical information for the frame (correlation matrices        etc.)    -   2. Compute filter coefficients and decide on frame partitioning    -   3. Read a whole frame in order to apply the computed filters on        the frame.

Accordingly, the frame-based filter estimation requires two whole frameaccesses in order to design and apply a filter. It has to be noted thatexternal memory access bandwidth is generally a very limited resource.

The details of the LCU-based parameter syntax structures of ALF and SAOcan be found in prior art document [3]. Further details with respect toLCU-based SAO are found in standard document JCTVC-H273, and furtherdetails regarding LCU-based ALF and SAO can be found in standarddocument JCTVC-H274_r2.

A general example for LCU-based parameter syntax structure is shownbelow:

for (i=0 ; i<num_LCUs_in_frame; i++) {  ALF_parameter_LCU_unit( ); }ALF_parameter_LCU_unit( ) {  ALF_on/off_flag;   //filtering is appliedin the current LCU or not.    if (ALF_on/off_flag == 1)     ALF_new_filter_flag;  //A new filter is    generated or a filterthat is generated in a previous LCU is used.    if (ALF_new_filter_flag)     filter_coefficients( );    else     use_filter_from_left_or_up_LCU_flag;    //Use the filter from leftLCU or upper LCU. }

In accordance therewith (cf. the for-loop), a filter parameter unit issignaled for each LCU.

The LCU-based filter estimation process can be summarized in thefollowing three steps:

-   -   1. Read LCU from memory. Compute statistical information.    -   2. According to a rate-distortion measure, decide on whether to        generate a new filter or to use an old filter that has been        generated in a previous LCU (previous in the coding order).    -   3. Apply the generated or re-used filter on the LCU.

FIG. 3 provides an illustration of an LCU-based syntax example for thecase of SAO (cf. prior art reference [1]). “SAOP” in the drawing meansSAO Parameter Unit. Thus, FIG. 3 illustrates four parameter units, SAOP1to SAOP4. For instance, in the case of SAO parameter unit 1, the SAOparameters are generated in the first LCU and the same filter parametersare applied on the first three LCUs in the same LCU row. In the secondand third LCUs in the row only one flag is needed to be signaledindicating that the same filter coefficients that are applied to leftLCU are applied to the current LCU. In a similar manner, the parametersof SAO parameter unit 2 (SAOP2) are, for instance, employed for the lasttwo parameter units in the first line, and the two parameter unitsbelow. In this example last two LCUs in the second LCU row signal a flagindicating that the SAO filter coefficients are inherited from the upperLCU. As compared to LCU-based filter estimation, frame-based parameterestimation causes increased encoding delay and external memory access.However, it is a more precise filter estimation method and results in abetter coding efficiency in subjective quality.

LCU-based parameter set estimation can be applied on the fly. Generally,the encoders operate on an LCU-basis, and therefore LCU-based filterestimation does not cost additional external memory access or additionalencoding delay. However, the coding efficiency is inferior, sinceparameter estimation is not good (most of the LCUs re-use previouslygenerated filters in order to reduce overhead).

Frame-based parameter syntax only allows frame-based filter estimation.However, LCU-based syntax allows both LCU- and frame-based estimation.

When frame-based filter estimation is used, the filter parameters can berepresented by either LCU-based syntax structure or frame-based syntaxstructure. The coding efficiency of the frame-based representation ishigher than that of LCU-based syntax, since LCU-based syntax incurs moreoverhead.

In the decoder, the filter application process is always the same,independent from the syntax structure or the filter estimation process.Therefore, before the actual decoding, on the decoder side, parsing ofreceived syntax structures has to be performed in order to retrieve theinformation about which filter parameters are to be applied for which ofthe LCUs.

The LCU-based parameter syntax of ALF and SAO can be placed (signaled)either in the adaptation parameter set (APS) or inside a slice.

For low delay applications, the filter parameters are signaled inside aslice. As a result, sub-picture level delay can be achieved by employingLCU-based filter estimation.

For non-low delay applications, the filter parameters might be signaledinside the APS. In this case, frame-based filter estimation can beapplied, resulting in a superior coding efficiency.

FIGS. 4, 5, and 6 illustrate the state of the art syntax structure forAPS, LCU-based SAO parameter set syntax, and LCU-based ALF parameter setsyntax.

FIG. 4 illustrates a table 400 comprising code lines which define atleast a part of the content of an APS element, called RBSP (Raw ByteSequence Payload). Specifically, code lines 401 to 405 containinformation relating to the SAO parameters, while code lines 406 to 408contain information relating to the ALF parameters. More specifically,code line 405 comprises the syntax element aps_sao_param( ) which may becoded with a CABAC encoding. Similarly, code line 408 comprises thesyntax element alf_param( ), which may also be coded with a VLC(Variable Length Code) or CABAC (Context Adapted Binary ArithmeticCoding) encoding. Accordingly, a single APS as defined by table 400 maycarry information relating to both ALF parameters and SAO parameters.

In the right hand column of table 400, descriptors indicate the type ofcoding which may be used for each of the syntax elements on the leftside of the table. The meaning of the descriptors to which reference ismade is defined in prior art documents [3] and [4]. The parsing processfor the respective descriptors is specified in section 9 of bothreferences [3] and [4].

In particular, the descriptors employed in FIG. 4 have the followingmeaning: ue(v) unsigned integer Exp-Golomb-coded syntax element with theleft bit first; u(n):unsigned integer using n bits. The parsing processfor this descriptor is specified by the return value of the functionread_bits(n) interpreted as a binary representation of an unsignedinteger with the most significant bit written first; se(v):signedinteger Exp-Golomb-coded syntax element with the left bit first.

FIG. 5 illustrates a table 500 comprising at least part of the syntaxelements of the sample adaptive offset parameter syntax structure, i.e.the function aps_sao_param( ) shown in line 405 of FIG. 4.

The parameters shown in lines 501 and 502 of the table of FIG. 5 arepresent in the parameter syntax structure if SAO parameters are signaledin the APS: sao_num_lcu_in_width_minus1 (501) andsao_num_lcu_in_height_minus1 (502). The value of(sao_num_lcu_in_width_minus1+1) specifies the number of coding treeblocks in picture widths. Parameter value(sao_num_lcu_in_height_minus1+1) specifies the number of coding treeblocks in picture height. As can be further seen from the syntax of FIG.5, these two parameter values specify the extent of two for-loops asdefined in lines 503 and 504 of FIG. 5. In accordance therewith, theamount of parameter units sao_unit_vlc( ) to be signaled for each LCUand including LCU-specific SAO filter and control parameters,illustrated in lines 505, 506, and 507 of FIG. 5, is thereby defined.

In a similar manner, FIG. 6 illustrates a table 600 comprising at leastpart of the syntax elements of an adaptive loop filter parameter syntaxstructure, i.e. corresponding to the function alf_param( ) of line 408of FIG. 4. Specifically, lines 601 and 602 include parametersalf_num_lcu_in_width_minus1 and alf_num_lcu_in_height_minus1. The value(alf_num_lcu_in_width_minus1+1) specifies the number of coding treeblocks of picture width. Variable numCtbInWidth is set to said value, ifit present. If, otherwise, alf_num_lcu_in_width_minus1 is not present,numCtbInWidth is set to PicWidthInCtbs.

Parameter value (alf_num_lcu_in_height_minus1+1) specifies the number ofcoding tree blocks of picture height. If the latter syntax element ispresent, numCtbInHeight is set equal to(alf_num_lcu_in_height_minus1+1). Otherwise, ifalf_num_lcu_in_height_minus1 is not present, numCtbInHeight is set equalto PicHeightInCtbs.

The latter syntax elements are present in the parameter syntaxstructure, if ALF parameters are signaled in the APS. As can be seenfrom the for-loop initiated at line 604 of FIG. 6, they define thenumber of parameter units alf_unit( ) which are in accordance with thestate of the art LCU-based ALF syntax are signaled for each LCU, andinclude LCU-specific ALF filter and control parameters.

As shown in the foregoing FIGS. 5 and 6, the number of the LCU-specificparameter units sao_unit_vlc( ) and alf_unit( ) can be derived based onthe syntax elements (sao_num_lcu_in_width_minus1,sao_num_lcu_in_height_minus1) and (alf_num_lcu_in_width_minus1,alf_num_lcu_in_height_minus1), respectively.

Therefore, the latter syntax elements have to be signalled in orderguarantee independent parsing of the APS, although in the state of theart syntax structures they basically represent duplicate informationsince they are also signalled in the SPS. Namely, it has to be notedthat an APS does not have any reference to a Sequence Parameter Set(SPS, including information on width, height and number of coding unitsof a frame), or to a Picture Parameter Set (PPS). Therefore, the widthand height of the coded picture or the LCU is not known in the APS. As aresult, in order to be able to parse an APS independent of an SPS orPPS, the four syntax elements shown in lines 501, 502 and 601, 602 ofFIGS. 5 and 6, respectively, need to be signalled in the APS, althoughit is a duplication of information.

As summarized above, the LCU-based syntax, although superior toframe-based syntax with respect to encoding delay and external memoryaccess requirements in the encoder, has the drawback of an increasedoverhead since an LCU parameter unit is signalled for each LCU. Thisbecomes particularly evident with increasing frame size and/ordecreasing LCU size.

For example, if the LCU size is small (usual LCU size 64×64 pixels [lumasamples], minimum supported size 16×16 pixels), the overhead of theLCU-based filter parameter syntax would be quite high. As a result, SAOand ALF would perform very poorly.

It is therefore desirable to amend the employed syntax structures insuch a manner that the signalling overhead is reduced, while maintainingthe advantages of LCU-based syntax as far as possible.

As a straightforward solution, one might consider using LCU-based syntaxonly when parameters are signalled inside the slice (i.e. for low-delayapplications), while employing frame-based syntax when parameters aresignalled in the APS. As a result, the overhead can be reduced in thecase of frame-based filter parameter estimation, when filter parametersare placed in the APS.

However, such a rather straightforward approach would create a newproblem: if two different syntax structures are used within the same bitstream, two different circuitries would have to be implemented in thedecoder unit, thereby increasing the number of logic gates, i.e. thehardware effort, and as a result, the overall cost.

In view of the above, it is therefore further desirable to reduce thesignalling overhead of LCU-based filter parameter signalling, in theparticular case of signalling within the APS (Adaptation Parameter Set).Such a solution is achieved by the present invention. Hence, althoughLCU-based parameter syntax structures can generally be placed withinAPS, as well as within a picture slice, the present invention dealsspecifically with the former case, i.e. a structure wherein the filterparameters are signalled within the APS.

If the ALF and SAO parameters are signalled within the picture slice,the control parameters and filter coefficients are coded with CABACentropy coding method. Since the CABAC has a context adaptive nature itcan effectively reduce the redundancy that is introduced by theLCU-based syntax.

However inside the APS the filter parameters are coded with VariableLength Coding. In this coding method the syntax elements of theLCU-based syntax structure are coded with variable length codesindependently (not jointly as in the case of CABAC coding). Thereforealthough the filter control parameters of neighbouring LCUs are similar,this redundancy cannot be exploited when parameters are coded inside anAPS.

The basic idea underlying the solution according to the presentinvention is to reduce the above described redundancy (duplication) ofinformation, but rather increase the information content of the existingsyntax elements of the LCU-based syntax structure.

In order to achieve said goal, filter parameter syntax units of theLCU-based syntax structure are adaptively grouped together in order toreduce overhead. Thereby, the LCU-based syntax representation is notchanged, but the effective region of the filter parameter syntax unitsis adaptively adjusted to be a group of LCUs (instead of a single LCU inthe state of the art). The region sizes are adaptively selected. Thiscan be done, for instance, based on a rate-distortion measure.

First of all, in order to represent the adaptive grouping information,additional syntax elements would be required. However, in accordancewith the present invention further considerations have been made toexploit the redundancies in the existing syntax elements. As a result,no additional syntax elements are required to be signalled, but theinformation content of the existing syntax elements is increased.

FIG. 7 illustrates an example of an excerpt of a table 500′ withadditional syntax elements in accordance with the basic idea underlyingthe present invention as outlined above. More specifically, table 500′relates to the function aps_sao_param( ) 405, the conventional syntax ofwhich has been illustrated by means of table 500 in FIG. 5.

Table 500′ of FIG. 7 differs from table 500 of FIG. 5 in that inside thesyntax structure of the SAO parameter set, besides syntax elements 501and 502, two new syntax elements are signalled in lines 701 and 702.Syntax element 701, labelled vertical_lcu_grouping_minus1 represents thenumber of LCUs that are grouped together in the vertical direction.Syntax element 702, labelled horizontal_lcu_grouping_minus1 representsthe number of LCUs that are grouped together in the horizontaldirection.

With the modification illustrated in FIG. 7, the following can beachieved: while according to the state of the art syntax structure (FIG.5) one parameter unit has to be signalled for each LCU, with themodification of FIG. 7 LCUs can be grouped together and one parameterunit must be signalled only for each LCU unit. As result, the signallingoverhead is reduced.

The approach of the present invention is especially useful in the caseof frame-based encoding. It has to be noted that the parsing of thesyntax structure aps_sao_param( ) 405 is the same as in the conventionalapproach. Therefore, in contrast to the “straightforward solution”mentioned above, no additional (second) parsing circuitry is required atthe decoder side.

Although FIG. 7 illustrates the modified syntax structure for the caseof Sample Adaptive Offset parameter syntax, this has been done by way ofexample only, and a person skilled in the art is aware that respectivemodifications apply to the syntax structures for encoding andtransmitting filter parameters for other kinds of filters, and inparticular for the Adaptive Loop Filter (ALF) parameter syntax.

FIG. 8 illustrates a second step of consideration to be performed forgenerating a syntactic structure in accordance with the presentinvention, namely wherein the number of syntax elements is reduced backto the number of syntax elements in conventional LCU-based signalling,while, however, the information content is changed to reduce redundancyand employ the available parameters more efficiently to reduce overhead.More specifically, in accordance with the present invention (as oncemore exemplified by means of SAO parameters), two new syntax elementsare derived based on the state of the art syntax elements 501 and 502and the newly introduced syntax elements 701 and 702 shown in FIG. 7.

The left hand side of FIG. 8 illustrates once more a part of syntaxtable 500′ of FIG. 7. As explained above, the syntax elementssao_num_lcu_in_width_minus1 (501) and sao_num_lcu_in_height_minus1 (502)are signaled inside the function aps_sao_param( ) 405 for the purpose ofindependent parsing of the APS. These syntax elements are used tocompute the number of SAO parameter units in the aps_sao_param( ). Asexplained above with reference to FIG. 5, the two syntax elements 501and 502 are used to deduce the number of parameter units sao_unit_vlc( )in the APS.

In the framework of the present invention, syntax elements 501 and 502are combined with newly introduced syntax elements 701 and 702 definingLCU grouping to result in two new syntax elements in the lines labeled501″ and 502″ of the further modified table 500″ shown on the right handside of FIG. 8. Namely, syntax element 501 and 701 on the one hand, and502 and 702, on the other hand, are combined into single syntax elements501″ and 502″, respectively in accordance with the relations:

aps_num_sao_unit_in_width_minus1=function(sao_num_lcu_in_width_minus1,horizontal_lcu_grouping_minus1)

aps_num_sao_unit_in_height_minus1=function(sao_num_lcu_in_height_minus1,vertical_lcu_grouping_minus1).

The two resulting parameters 501″ and 502″ provide all necessaryinformation to correctly parse the bit stream at the decoder side. Thefunction which is only generally indicated in the above relations maybe, for example, division of parameters followed by any of the standardfunctions round( ), ceil( ), floor( ) as defined, for instance in priorart reference [3].

In accordance therewith, ceil(x) is the smallest integer greater than orequal to x; floor(x) is the greatest integer less than or equal to x;and round(x)=sign(x)*floor(abs(x)+0.5).

However, the function is not limited to the above described examples,and a custom defined function or function that is indicated or signalledinside the bit stream is also applicable within the framework of thepresent invention.

The meaning of the combined parameters 501″ and 502″ is as follows:

(aps_num_sao_unit_in_width_minus1+1) specifies the number of SampleAdaptive Offset units in picture width.(aps_num_sao_unit_in_height_minus1+1) specifies the number of SampleAdaptive Offset units in picture height. In accordance with the presentinvention, syntax elements 501″ and 502″ replace conventional syntaxelements 501 and 502. In other words, a new use is given for the syntaxelements provided in the respective place of the function aps_sao_param() 405. While the syntax elements sao_num_lcu_in_width_minus1 (501) andsao_num_lcu_in_height_minus1 (502) which are required for parsing of theAPS basically provide duplicate information in the bit stream,respective new syntax elements 501″ and 502″ are not redundant anymore.

More generally, new syntax elements 501″ and 502″ specify the number ofLCU groups (filter parameter signalling units) in the direction ofpicture width (frame width) and in the direction of picture height(frame hight), respectively. They are generated based on syntax elements(501 and 502) specifying the number of LCUs per picture (in width andheight direction, respectively) and syntax elements (701 and 702)specifying the number of LCUs that are grouped together (in vertical andhorizontal direction, respectively). More specifically, syntax elements501″ and 502″ are generated by applying a predetermined function onsyntax elements 501, 502, 701 and 702.

Based on the number of LCU groups and the number of LCUs per picture(frame), a mapping function is applied to determine which LCUs of theframe exactly are grouped together, thereby determining the correctfilter parameters for each single LCU. The mapping function may be astandard or customized function, which may be preset on the decoder sidefor proper parsing. Alternatively, information specifying thepredetermined function may be encoded in the bitstream for beingtransmitted to the decoder side. At the decoder side, the mappingfunction is applied to determine which of the filter parameters to applyto a particular LCU, by determining the LCU group to which it belongs.Further details regarding the mapping function are described below.

As indicated above, although the detailed illustration is providedherein with respect to function aps_sao_param( ) 405, a person skilledin the art is aware on how to modify respective structures for otherkinds of filter parameters. In particular, for the function alf_param( )408 illustrated for the conventional case in FIG. 6, parameters 601 and602 combine with the new information contained in parameters 701 and 702to form new syntax elements aps_num_alf_unit_in_width_minus1 andaps_num_alf_unit_in_height_minus1. Herein, the value(aps_num_alf_unit_in_width_minus1+1) specifies the number of AdaptiveLoop Filter units in picture width. If the parameter is present, thevariable numCtbInWidth is set to (aps_num_alf_unit_in_width_minus1+1).Otherwise, if the parameter aps_num_alf_unit_in_width_minus1 is notpresent, numCtbInWidth is set to PicWidthInCtbs. The parameter value(aps_num_alf_unit_in_height_minus1+1) specifies the number of adaptiveloop filter units and picture height. The variable numCtbInHeight is setto (aps_num_alf_unit_in_height_minus1+1), ifaps_num_alf_unit_in_height_minus1 is present. Otherwise, numCtbInHeightis set to PicHeightInCtbs.

A more complete illustration of modified table 500″ illustrating sampleadaptive offset parameter syntax in accordance with the presentinvention, by way of example, is shown in FIG. 9. As can be seen fromFIG. 9, function aps_sao_param( ) 405 has been modified by replacinglines 501 and 502 of the corresponding state of the art syntaxillustrated in FIG. 5 with lines 501″ and 502″ that have been explainedabove with reference to FIG. 8. As a consequence, lines 503 and 504 ofFIG. 5 defining the two for-loops within which the parameter units aredefined have been modified to lines 503″ and 504″. In the latter lines,as can be seen from FIG. 9, the parameters(sao_num_lcu_in_height(width)_minus1+1) have been replaced by theparameters (aps_num_sao_unit_in_height(width)_minus1+1) in thedefinition of the for-loops. As a consequence, the number of parameterunits sao_unit_vlc( ) in lines 506, 507, and 508 is now defined by thenewly introduced parameters specifying the number of SAO units, i.e. LCUgroups.

As can be seen from the above, the present invention breaks theone-to-one mapping of filter parameter units to LCUs, in view of the LCUgrouping. Since, moreover, the structure of the present invention,without employing extra syntax elements, does not signal LCU groupinginformation explicitly, the LCU grouping information (in the illustratedexamples: for instance in the vertical and horizontal direction) has tobe inferred on the decoder side, in order to apply SAO and ALF correctlyon a picture slice.

In other words: in the decoder, information has to be generatedspecifying “which filter parameter set is applied to which LCU”, inorder to correctly apply filtering in the decoding processing of FIG. 2.Therefore, a mapping rule is necessary, which is provided by the mappingfunction mentioned above.

As a consequence, the bit stream must be parsed at the decoder side,before the actual decoding can be performed. Therefore, the slice headerhas reference to an SPS and an APS. This is illustrated in FIG. 10.

As described above, in the APS, the number of SAO parameter units perframe in picture width and height is available. Moreover, in the SPS,the number of LCUs in picture width and height is available, which is nolonger present in the APS as modified in accordance with the presentinvention. As a consequence, as soon as a slice header is available forparsing, the number of LCUs per frame is known, and the mapping of theparameters to the individual LCUs in a slice can be computed whenever aslice is available.

More generally, the picture slice header is a third syntax structureincluding references to a first syntax structure (APS) and a secondsyntax structure (SPS). From the first syntax structure, informationspecifying the number of LCU groups (in a picture width and heightdirection) can be retrieved. From the second syntax structure,information specifying the number of LCUs can be retrieved.

A flow chart illustrating the decoder side processing in accordance withthe present invention is shown in FIG. 11.

In the first step 1120, a picture slice header identified in the encodedbit stream 1110 is parsed. As indicated above, the slice header hasreferences to an SPS and an APS. (Further, the slice header also refersto a picture parameter set PPS, which is, however, not essential for thepresent invention).

Firstly, the slice header refers to the SPS. As a result of parsing theSPS referred to in step 1130, the width and height of the frame and theLCU are known in the slice. As a consequence, the number of LCUs perframe can be determined.

Secondly, the slice header refers to the APS. As a result of parsing APSin step 1140, the number of filter units per width and height are knownin the slice.

As a consequence, after performing steps 1130 and 1140, the filterparameters in the APS can be mapped to each LCU in the slice, which isperformed in subsequent step 1150 of FIG. 11. In other words, thenecessary information to infer which filter parameter set is to beapplied to which LCU is available, although the present inventionapplies signalling on APS level only, but not on the slice level.

Generally speaking, the mapping function is applied in step 1150, in thedecoder. The mapping function uses the following information:aps_num_alf_unit_in_height_minus1 and aps_num_alf_unit_in_width_minus1(from APS, in the present case exemplified for ALF, applicable in ananalog manner to SAO); frame height, frame width, LCU height and LCUwidth from SPS. The mapping function provides the information specifyingwhich filter parameter set is applied to which LCU.

Generally, the mapping function determines the filter parameters thatare used in the LCU as a function of the arguments lcu_x and lcu_y(specifying the coordinates of the current LCU),aps_num_alf_unit_in_height_minus1, aps_num_alf_unit_in_width_minus1,frame height, frame width, LCU height, LCU width:

(Filter parameters that are used in the LCU)=function(lcu_(—) x,lcu_(—)y,aps_num_alf_unit_in_height_minus1,aps_num_alf_unit_in_width_minus1,frameheight,frame width,LCU height,LCU width).

The function itself may be, for instance, one of functions round( )ceil( ) floor( ) as defined in prior art document [3]. Also, any customdefined function that has been preset in the decoder in advance ispossible. Alternatively, the function may be indicated or signalledexplicitly inside the bit stream.

In other words, the present invention provides a virtual image plane forfilter parameter sets. In set 1150 of FIG. 11, the virtual filter planeis mapped to the actual coded picture. Only after step 1150, the actualdecoding of the pictures included in the bit stream, including filterapplication, is possible to be performed in subsequent step 1160. As aresult, sequence of images 1170 is available on the decoder side.

In the following, two different mapping functions that have beendeveloped in the present invention, are explained in detail withreference to FIGS. 12, 13 and 14. The exemplary mapping functions givenherein by way of example for the case of SAO are mutatis mutandisapplicable to other filter variable filter parameters, and in particularto ALF. The mapping functions are employed both for LCU grouping(partitioning a LCU frame into groups) at the encoder side as well asfor allocating the correct filter parameters to the LCU units on thedecoder side.

In accordance with a first example of a mapping function, the followingtwo rules are applied:

-   1. Partition a frame into equally spaced regions where the region    height and the region width are given by

region height=frame height/(aps_num_sao_unit_in_height_minus1+1)

region width=frame width/(aps_num_sao_unit_in_width_minus1+1)

-   2. Determine the center point for each LCU. An LCU is assigned to a    region if its center point lies inside that region.

Each of said regions corresponds to one of the LCU groups of the presentinvention, so that the number of SAO parameter units that are signalledin the APS is equal to the number of regions.

LCU grouping in accordance with the above described rules 1 and 2 isillustrated in an exemplary manner in FIG. 12. In the figure, by way ofexample, a frame with a height of 256 luma samples (or chroma samples)and a width of 352 luma samples (or chroma samples) is illustrated. TheLCU height and LCU width is 64 luma samples each. As a consequence,there are twenty four LCUs, which are arranged in four lines. The LCUboundaries are indicated by full horizontal and vertical lines. It hasto be noted that the rightmost LCU of each line does not form a completeLCU, since the frame width of 352 is no integer multiple of the LCUwidth of 64. Actually, there are 5.5 LCU widths per line. A black fulldot in each LCU in FIG. 12 indicates the center point for the respectiveLCU.

Moreover, in FIG. 12 it is assumed thataps_num_sao_unit_in_height_minus1=2 and theaps_num_sao_unit_in_width_minus1=3. This means that there are three SAOunits in height direction, and four SAO units in width direction. In thefigure, the dashed lines represent the boundaries of the SAO units(region boundaries), before having been aligned with LCU boundaries.

The result of the applying of the first exemplary mapping function inthe example of FIG. 12 is shown in FIG. 13. Namely, FIG. 13 shows theresulting LCU groups (SAO units) according to an LCU grouping method ofthe first exemplary mapping function.

The result of applying said mapping function are LCU groups the areasizes of which are close to each other. Such a property is desirablesince it facilitates region filter adaptation. However, the resultingregion sizes are still not exactly equal to each other, due to therequirement that the filter regions should be aligned with the LCUboundaries. The illustrated mapping function takes into account the factthat there can be incomplete LCUs at the right and bottom frameboundaries (in the present case: at the right boundary).

In FIG. 13, SAO unit boundaries are once more shown by dashed lines.Since they coincide with LCU boundaries, the SAO unit boundaries areshown in FIG. 13 by an overlay of a thin full line and a slightly widerdashed line. LCU boundaries that are not SAO unit boundaries at the sametime, are shown as thin full lines only.

More specifically, the operation for obtaining the result of FIG. 13based on the input illustrated in FIG. 12 by means of the rules of thefirst exemplary mapping function, will be described below. In accordancewith FIG. 12, the inputs of the derivation process are a luma location(xC, yC), specifying the top-left luma sample of a current LargestCoding Unit (LCU) relative to the top-left luma sample of the currentpicture, a parameter regionHeight that is set equal to the value (frameheight/(aps_num_sao_unit_in_height_minus1+1)), a parameter regionWidththat is set equal to the value of (framewidth/(aps_num_sao_unit_in_width_minus1+1), a parameter lcuWidthspecifying the width of the current LCU in luma samples, and a parameterlcuHeight specifying the height of the current LCU in luma samples.

As output of the derivation process are derived parameters saoUnitId_xand saoUnitId_y, which describe the index of the SAO parameter unit inthe x- and y-directions. Although parameters are defined in accordancewith the equations

saoUnitId_(—) x=round((lcuWidth/2+xC)/regionWidth)

saoUnitId_(—) y=round((lcuHeight/2+yC)/regionHeight)

In the syntax structure of the present invention, illustrated in FIG. 9,the filter parameter unit applied to the current LCU is given bysao_unit_vlc(saoUnitId_x,saoUnitId_y,0).

It is noted that instead of the round( ) function, a ceil( ) or floor( )can be used as well.

An alternative second example of a mapping function will be illustratedbelow with reference to FIG. 14.

The mapping function in accordance with the second example applies thefollowing two rules:

-   1. Find the width and height of the LCU groups based on the number    of LCUs (illustrated in FIG. 12) as follows:

lcuGroupHeight=floor(number of LCU in pictureheight/(aps_num_sao_unit_in_height_minus1+1))

lcuGroupWidth=floor(number of LCU in picturewidth/(aps_num_sao_unit_in_width_minus1+1))

It is noted that instead of the floor( ) function, a ceil( ) or round( )can be used as well.

-   2. Assigning the LCU to an SAO parameter unit using the following    equations:

saoUnitItId_(—) x=min(ceil(lcu_(—)x/lcuGroupWidth),(aps_num_sao_unit_in_width_minus1+1))

saoUnitId_(—) y=min(ceil(lcu_(—)y/lcuGroupHeight),(aps_num_sao_unit_in_height_minus1+1)).

In the foregoing equations, lcu_x and lcu_y mean the coordinates of acurrent LCU (i.e. the sequential number of the LCU counted from theright top LCU having co-ordinates (lcu_x, lcu_y)=(1, 1)). It is furthernoted that instead of the ceil( ) function, floor( ) or round( )functions are equally applicable.

In the syntax structure of the present invention, illustrated in FIG. 9,the filter parameter unit applied to the current LCU is given bysao_unit_vlc(saoUnitId_x,saoUnitId_y,0).

The LCU groups resulting from applying the second exemplary mappingfunction on the frame as illustrated in FIG. 12 is shown in FIG. 14. Ascan be seen therefrom, the resulting LCU groups (SAO units) aredifferent to those derived in FIG. 13, based on the first exemplarymapping function. In particular, the sizes of the filtering regionsdiffer more from each other in accordance with the second exemplarymapping function of FIG. 14, as compared to the first exemplary mappingfunction of FIG. 13. However, the second exemplary mapping functionallows an easier implementation in some commonly used architectures.

The same mapping function that is used in the decoder should be used inthe encoder for frame partitioning as well in order to achieve identicalreconstructed images. The encoder would be implemented in such a waythat it tries all LCU grouping possibilities that can be achieved by themapping function, and picks the best LCU grouping possibility. Thecomparison of the LCU grouping possibilities can be based on a costfunction according to a rate-distortion measure. In other words the LCUgroup size can be decided by the encoder based on the following rate anddistortion measures:

-   -   bitrate increase associated with transmission of filter        parameters and    -   the amount of reduction in the coding noise resulting from the        filtering operation.

In the following, the main benefit that can be achieved by means of thepresent invention will be summarized.

Firstly, the extensive overhead of LCU-based filter parameter syntax canbe mitigated. Especially, when the LCU size is small, multiple LCUs canbe grouped together in rectangular filter units restricting the overheadof parameter sets over a larger filter design area.

Usually, frame-based filter parameter estimation is applied when thefilter parameters are signaled in the APS. The invented mapping schemeof filter parameters offers the possibility of partitioning a frame intoregions of multiple LCUs, where a single parameter unit is generated foreach region. Therefore, the scheme in accordance with the presentinvention reduces the parameter signaling overhead and is more suitablefor frame-based filter estimation process.

In addition, with the help of the scheme of the invention, the filterparameters (in particular: SAO and ALF parameters) can be signaled inthe APS independent of the actual frame sizes since the filterparameters are later mapped to the actual frame. Therefore, with thehelp of the scheme according to the present invention, a scalable codingis supported automatically.

In the case of spatial scalability, the video sequence contains picturesof multiple sizes. The filter parameters in the same APS can be mappedto different frames in a sequence with different frame sizes.

As a result, filter parameters that are signaled in the APS can be usedby both lower resolution and higher resolution pictures in the scalablevideo sequence. The latter additional improvement that can be achievedby means of the present invention is illustrated in FIG. 15. On the lefthand side of FIG. 15, the situation in accordance with the state of theart is illustrated. Since the same APS cannot be referred to bydifferent resolution layers, in the state of the art APS 1 is notapplicable to slice 2 corresponding to higher resolution.

In contrast, since in accordance with the present invention the same APScan be referred to by different resolution layers, in the presentinvention APS 1 also supports slice 2 corresponding to higherresolution, as illustrated on the right hand side of FIG. 15.

Finally, with the help of the scheme of the invention, the filterparameters (in particular: SAO and ALF parameters) that are signaled inan APS can be used by different picture slices that have different LCUand picture sizes. In particular in a video coded bitstream twodifferent picture slices can have different LCU and frame sizes whichare determined by an SPS. Since filter parameters are signaledindependent from LCU and frame size, two different picture slices havingdifferent LCU or frame sizes can refer to the same APS and use the samefilter parameters.

The processing described in each of embodiments can be simplyimplemented in an independent computer system, by recording, in arecording medium, a program for implementing the configurations of themoving picture coding method (image coding method) and the movingpicture decoding method (image decoding method) described in each ofembodiments. The recording media may be any recording media as long asthe program can be recorded, such as a magnetic disk, an optical disk, amagnetic optical disk, an IC card, and a semiconductor memory.

Hereinafter, the applications to the moving picture coding method (imagecoding method) and the moving picture decoding method (image decodingmethod) described in each of embodiments and systems using thereof willbe described. The system has a feature of having an image coding anddecoding apparatus that includes an image coding apparatus using theimage coding method and an image decoding apparatus using the imagedecoding method. Other configurations in the system can be changed asappropriate depending on the cases.

Embodiment A

FIG. 16 illustrates an overall configuration of a content providingsystem ex100 for implementing content distribution services. The areafor providing communication services is divided into cells of desiredsize, and base stations ex106, ex107, ex108, ex109, and ex110 which arefixed wireless stations are placed in each of the cells.

The content providing system ex100 is connected to devices, such as acomputer ex111, a personal digital assistant (PDA) ex112, a cameraex113, a cellular phone ex114 and a game machine ex115, via the Internetex101, an Internet service provider ex102, a telephone network ex104, aswell as the base stations ex106 to ex110, respectively.

However, the configuration of the content providing system ex100 is notlimited to the configuration shown in FIG. 16, and a combination inwhich any of the elements are connected is acceptable. In addition, eachdevice may be directly connected to the telephone network ex104, ratherthan via the base stations ex106 to ex110 which are the fixed wirelessstations. Furthermore, the devices may be interconnected to each othervia a short distance wireless communication and others.

The camera ex113, such as a digital video camera, is capable ofcapturing video. A camera ex116, such as a digital camera, is capable ofcapturing both still images and video. Furthermore, the cellular phoneex114 may be the one that meets any of the standards such as GlobalSystem for Mobile Communications (GSM) (registered trademark), CodeDivision Multiple Access (CDMA), Wideband-Code Division Multiple Access(W-CDMA), Long Term Evolution (LTE), and High Speed Packet Access(HSPA). Alternatively, the cellular phone ex114 may be a PersonalHandyphone System (PHS).

In the content providing system ex100, a streaming server ex103 isconnected to the camera ex113 and others via the telephone network ex104and the base station ex109, which enables distribution of images of alive show and others. In such a distribution, a content (for example,video of a music live show) captured by the user using the camera ex113is coded as described above in each of embodiments (i.e., the camerafunctions as the image coding apparatus according to an aspect of thepresent invention), and the coded content is transmitted to thestreaming server ex103. On the other hand, the streaming server ex103carries out stream distribution of the transmitted content data to theclients upon their requests. The clients include the computer ex111, thePDA ex112, the camera ex113, the cellular phone ex114, and the gamemachine ex115 that are capable of decoding the above-mentioned codeddata. Each of the devices that have received the distributed datadecodes and reproduces the coded data (i.e., functions as the imagedecoding apparatus according to an aspect of the present invention).

The captured data may be coded by the camera ex113 or the streamingserver ex103 that transmits the data, or the coding processes may beshared between the camera ex113 and the streaming server ex103.Similarly, the distributed data may be decoded by the clients or thestreaming server ex103, or the decoding processes may be shared betweenthe clients and the streaming server ex103. Furthermore, the data of thestill images and video captured by not only the camera ex113 but alsothe camera ex116 may be transmitted to the streaming server ex103through the computer ex111. The coding processes may be performed by thecamera ex116, the computer ex111, or the streaming server ex103, orshared among them.

Furthermore, the coding and decoding processes may be performed by anLSI ex500 generally included in each of the computer ex111 and thedevices. The LSI ex500 may be configured of a single chip or a pluralityof chips. Software for coding and decoding video may be integrated intosome type of a recording medium (such as a CD-ROM, a flexible disk, anda hard disk) that is readable by the computer ex111 and others, and thecoding and decoding processes may be performed using the software.Furthermore, when the cellular phone ex114 is equipped with a camera,the video data obtained by the camera may be transmitted. The video datais data coded by the LSI ex500 included in the cellular phone ex114.

Furthermore, the streaming server ex103 may be composed of servers andcomputers, and may decentralize data and process the decentralized data,record, or distribute data.

As described above, the clients may receive and reproduce the coded datain the content providing system ex100. In other words, the clients canreceive and decode information transmitted by the user, and reproducethe decoded data in real time in the content providing system ex100, sothat the user who does not have any particular right and equipment canimplement personal broadcasting.

Aside from the example of the content providing system ex100, at leastone of the moving picture coding apparatus (image coding apparatus) andthe moving picture decoding apparatus (image decoding apparatus)described in each of embodiments may be implemented in a digitalbroadcasting system ex200 illustrated in FIG. 17. More specifically, abroadcast station ex201 communicates or transmits, via radio waves to abroadcast satellite ex202, multiplexed data obtained by multiplexingaudio data and others onto video data. The video data is data coded bythe moving picture coding method described in each of embodiments (i.e.,data coded by the image coding apparatus according to an aspect of thepresent invention). Upon receipt of the multiplexed data, the broadcastsatellite ex202 transmits radio waves for broadcasting. Then, a home-useantenna ex204 with a satellite broadcast reception function receives theradio waves. Next, a device such as a television (receiver) ex300 and aset top box (STB) ex217 decodes the received multiplexed data, andreproduces the decoded data (i.e., functions as the image decodingapparatus according to an aspect of the present invention).

Furthermore, a reader/recorder ex218 (i) reads and decodes themultiplexed data recorded on a recording medium ex215, such as a DVD anda BD, or (i) codes video signals in the recording medium ex215, and insome cases, writes data obtained by multiplexing an audio signal on thecoded data. The reader/recorder ex218 can include the moving picturedecoding apparatus or the moving picture coding apparatus as shown ineach of embodiments. In this case, the reproduced video signals aredisplayed on the monitor ex219, and can be reproduced by another deviceor system using the recording medium ex215 on which the multiplexed datais recorded. It is also possible to implement the moving picturedecoding apparatus in the set top box ex217 connected to the cable ex203for a cable television or to the antenna ex204 for satellite and/orterrestrial broadcasting, so as to display the video signals on themonitor ex219 of the television ex300. The moving picture decodingapparatus may be implemented not in the set top box but in thetelevision ex300.

FIG. 18 illustrates the television (receiver) ex300 that uses the movingpicture coding method and the moving picture decoding method describedin each of embodiments. The television ex300 includes: a tuner ex301that obtains or provides multiplexed data obtained by multiplexing audiodata onto video data, through the antenna ex204 or the cable ex203, etc.that receives a broadcast; a modulation/demodulation unit ex302 thatdemodulates the received multiplexed data or modulates data intomultiplexed data to be supplied outside; and amultiplexing/demultiplexing unit ex303 that demultiplexes the modulatedmultiplexed data into video data and audio data, or multiplexes videodata and audio data coded by a signal processing unit ex306 into data.

The television ex300 further includes: a signal processing unit ex306including an audio signal processing unit ex304 and a video signalprocessing unit ex305 that decode audio data and video data and codeaudio data and video data, respectively (which function as the imagecoding apparatus and the image decoding apparatus according to theaspects of the present invention); and an output unit ex309 including aspeaker ex307 that provides the decoded audio signal, and a display unitex308 that displays the decoded video signal, such as a display.Furthermore, the television ex300 includes an interface unit ex317including an operation input unit ex312 that receives an input of a useroperation. Furthermore, the television ex300 includes a control unitex310 that controls overall each constituent element of the televisionex300, and a power supply circuit unit ex311 that supplies power to eachof the elements. Other than the operation input unit ex312, theinterface unit ex317 may include: a bridge ex313 that is connected to anexternal device, such as the reader/recorder ex218; a slot unit ex314for enabling attachment of the recording medium ex216, such as an SDcard; a driver ex315 to be connected to an external recording medium,such as a hard disk; and a modem ex316 to be connected to a telephonenetwork. Here, the recording medium ex216 can electrically recordinformation using a non-volatile/volatile semiconductor memory elementfor storage. The constituent elements of the television ex300 areconnected to each other through a synchronous bus.

First, the configuration in which the television ex300 decodesmultiplexed data obtained from outside through the antenna ex204 andothers and reproduces the decoded data will be described. In thetelevision ex300, upon a user operation through a remote controllerex220 and others, the multiplexing/demultiplexing unit ex303demultiplexes the multiplexed data demodulated by themodulation/demodulation unit ex302, under control of the control unitex310 including a CPU. Furthermore, the audio signal processing unitex304 decodes the demultiplexed audio data, and the video signalprocessing unit ex305 decodes the demultiplexed video data, using thedecoding method described in each of embodiments, in the televisionex300. The output unit ex309 provides the decoded video signal and audiosignal outside, respectively. When the output unit ex309 provides thevideo signal and the audio signal, the signals may be temporarily storedin buffers ex318 and ex319, and others so that the signals arereproduced in synchronization with each other. Furthermore, thetelevision ex300 may read multiplexed data not through a broadcast andothers but from the recording media ex215 and ex216, such as a magneticdisk, an optical disk, and a SD card. Next, a configuration in which thetelevision ex300 codes an audio signal and a video signal, and transmitsthe data outside or writes the data on a recording medium will bedescribed. In the television ex300, upon a user operation through theremote controller ex220 and others, the audio signal processing unitex304 codes an audio signal, and the video signal processing unit ex305codes a video signal, under control of the control unit ex310 using thecoding method described in each of embodiments. Themultiplexing/demultiplexing unit ex303 multiplexes the coded videosignal and audio signal, and provides the resulting signal outside. Whenthe multiplexing/demultiplexing unit ex303 multiplexes the video signaland the audio signal, the signals may be temporarily stored in thebuffers ex320 and ex321, and others so that the signals are reproducedin synchronization with each other. Here, the buffers ex318, ex319,ex320, and ex321 may be plural as illustrated, or at least one buffermay be shared in the television ex300. Furthermore, data may be storedin a buffer so that the system overflow and underflow may be avoidedbetween the modulation/demodulation unit ex302 and themultiplexing/demultiplexing unit ex303, for example.

Furthermore, the television ex300 may include a configuration forreceiving an AV input from a microphone or a camera other than theconfiguration for obtaining audio and video data from a broadcast or arecording medium, and may code the obtained data. Although thetelevision ex300 can code, multiplex, and provide outside data in thedescription, it may be capable of only receiving, decoding, andproviding outside data but not the coding, multiplexing, and providingoutside data.

Furthermore, when the reader/recorder ex218 reads or writes multiplexeddata from or on a recording medium, one of the television ex300 and thereader/recorder ex218 may decode or code the multiplexed data, and thetelevision ex300 and the reader/recorder ex218 may share the decoding orcoding.

As an example, FIG. 19 illustrates a configuration of an informationreproducing/recording unit ex400 when data is read or written from or onan optical disk. The information reproducing/recording unit ex400includes constituent elements ex401, ex402, ex403, ex404, ex405, ex406,and ex407 to be described hereinafter. The optical head ex401 irradiatesa laser spot in a recording surface of the recording medium ex215 thatis an optical disk to write information, and detects reflected lightfrom the recording surface of the recording medium ex215 to read theinformation. The modulation recording unit ex402 electrically drives asemiconductor laser included in the optical head ex401, and modulatesthe laser light according to recorded data. The reproductiondemodulating unit ex403 amplifies a reproduction signal obtained byelectrically detecting the reflected light from the recording surfaceusing a photo detector included in the optical head ex401, anddemodulates the reproduction signal by separating a signal componentrecorded on the recording medium ex215 to reproduce the necessaryinformation. The buffer ex404 temporarily holds the information to berecorded on the recording medium ex215 and the information reproducedfrom the recording medium ex215. The disk motor ex405 rotates therecording medium ex215. The servo control unit ex406 moves the opticalhead ex401 to a predetermined information track while controlling therotation drive of the disk motor ex405 so as to follow the laser spot.The system control unit ex407 controls overall the informationreproducing/recording unit ex400. The reading and writing processes canbe implemented by the system control unit ex407 using variousinformation stored in the buffer ex404 and generating and adding newinformation as necessary, and by the modulation recording unit ex402,the reproduction demodulating unit ex403, and the servo control unitex406 that record and reproduce information through the optical headex401 while being operated in a coordinated manner. The system controlunit ex407 includes, for example, a microprocessor, and executesprocessing by causing a computer to execute a program for read andwrite.

Although the optical head ex401 irradiates a laser spot in thedescription, it may perform high-density recording using near fieldlight.

FIG. 20 illustrates the recording medium ex215 that is the optical disk.On the recording surface of the recording medium ex215, guide groovesare spirally formed, and an information track ex230 records, in advance,address information indicating an absolute position on the diskaccording to change in a shape of the guide grooves. The addressinformation includes information for determining positions of recordingblocks ex231 that are a unit for recording data. Reproducing theinformation track ex230 and reading the address information in anapparatus that records and reproduces data can lead to determination ofthe positions of the recording blocks. Furthermore, the recording mediumex215 includes a data recording area ex233, an inner circumference areaex232, and an outer circumference area ex234. The data recording areaex233 is an area for use in recording the user data. The innercircumference area ex232 and the outer circumference area ex234 that areinside and outside of the data recording area ex233, respectively arefor specific use except for recording the user data. The informationreproducing/recording unit 400 reads and writes coded audio, coded videodata, or multiplexed data obtained by multiplexing the coded audio andvideo data, from and on the data recording area ex233 of the recordingmedium ex215.

Although an optical disk having a layer, such as a DVD and a BD isdescribed as an example in the description, the optical disk is notlimited to such, and may be an optical disk having a multilayerstructure and capable of being recorded on a part other than thesurface. Furthermore, the optical disk may have a structure formultidimensional recording/reproduction, such as recording ofinformation using light of colors with different wavelengths in the sameportion of the optical disk and for recording information havingdifferent layers from various angles.

Furthermore, a car ex210 having an antenna ex205 can receive data fromthe satellite ex202 and others, and reproduce video on a display devicesuch as a car navigation system ex211 set in the car ex210, in thedigital broadcasting system ex200. Here, a configuration of the carnavigation system ex211 will be a configuration, for example, includinga GPS receiving unit from the configuration illustrated in FIG. 18. Thesame will be true for the configuration of the computer ex111, thecellular phone ex114, and others.

FIG. 21A illustrates the cellular phone ex114 that uses the movingpicture coding method and the moving picture decoding method describedin embodiments. The cellular phone ex114 includes: an antenna ex350 fortransmitting and receiving radio waves through the base station ex110; acamera unit ex365 capable of capturing moving and still images; and adisplay unit ex358 such as a liquid crystal display for displaying thedata such as decoded video captured by the camera unit ex365 or receivedby the antenna ex350. The cellular phone ex114 further includes: a mainbody unit including an operation key unit ex366; an audio output unitex357 such as a speaker for output of audio; an audio input unit ex356such as a microphone for input of audio; a memory unit ex367 for storingcaptured video or still pictures, recorded audio, coded or decoded dataof the received video, the still pictures, e-mails, or others; and aslot unit ex364 that is an interface unit for a recording medium thatstores data in the same manner as the memory unit ex367.

Next, an example of a configuration of the cellular phone ex114 will bedescribed with reference to FIG. 21B. In the cellular phone ex114, amain control unit ex360 designed to control overall each unit of themain body including the display unit ex358 as well as the operation keyunit ex366 is connected mutually, via a synchronous bus ex370, to apower supply circuit unit ex361, an operation input control unit ex362,a video signal processing unit ex355, a camera interface unit ex363, aliquid crystal display (LCD) control unit ex359, amodulation/demodulation unit ex352, a multiplexing/demultiplexing unitex353, an audio signal processing unit ex354, the slot unit ex364, andthe memory unit ex367.

When a call-end key or a power key is turned ON by a user's operation,the power supply circuit unit ex361 supplies the respective units withpower from a battery pack so as to activate the cell phone ex114.

In the cellular phone ex114, the audio signal processing unit ex354converts the audio signals collected by the audio input unit ex356 invoice conversation mode into digital audio signals under the control ofthe main control unit ex360 including a CPU, ROM, and RAM. Then, themodulation/demodulation unit ex352 performs spread spectrum processingon the digital audio signals, and the transmitting and receiving unitex351 performs digital-to-analog conversion and frequency conversion onthe data, so as to transmit the resulting data via the antenna ex350.Also, in the cellular phone ex114, the transmitting and receiving unitex351 amplifies the data received by the antenna ex350 in voiceconversation mode and performs frequency conversion and theanalog-to-digital conversion on the data. Then, themodulation/demodulation unit ex352 performs inverse spread spectrumprocessing on the data, and the audio signal processing unit ex354converts it into analog audio signals, so as to output them via theaudio output unit ex357.

Furthermore, when an e-mail in data communication mode is transmitted,text data of the e-mail inputted by operating the operation key unitex366 and others of the main body is sent out to the main control unitex360 via the operation input control unit ex362. The main control unitex360 causes the modulation/demodulation unit ex352 to perform spreadspectrum processing on the text data, and the transmitting and receivingunit ex351 performs the digital-to-analog conversion and the frequencyconversion on the resulting data to transmit the data to the basestation ex110 via the antenna ex350. When an e-mail is received,processing that is approximately inverse to the processing fortransmitting an e-mail is performed on the received data, and theresulting data is provided to the display unit ex358.

When video, still images, or video and audio in data communication modeis or are transmitted, the video signal processing unit ex355 compressesand codes video signals supplied from the camera unit ex365 using themoving picture coding method shown in each of embodiments (i.e.,functions as the image coding apparatus according to the aspect of thepresent invention), and transmits the coded video data to themultiplexing/demultiplexing unit ex353. In contrast, during when thecamera unit ex365 captures video, still images, and others, the audiosignal processing unit ex354 codes audio signals collected by the audioinput unit ex356, and transmits the coded audio data to themultiplexing/demultiplexing unit ex353.

The multiplexing/demultiplexing unit ex353 multiplexes the coded videodata supplied from the video signal processing unit ex355 and the codedaudio data supplied from the audio signal processing unit ex354, using apredetermined method. Then, the modulation/demodulation unit(modulation/demodulation circuit unit) ex352 performs spread spectrumprocessing on the multiplexed data, and the transmitting and receivingunit ex351 performs digital-to-analog conversion and frequencyconversion on the data so as to transmit the resulting data via theantenna ex350.

When receiving data of a video file which is linked to a Web page andothers in data communication mode or when receiving an e-mail with videoand/or audio attached, in order to decode the multiplexed data receivedvia the antenna ex350, the multiplexing/demultiplexing unit ex353demultiplexes the multiplexed data into a video data bit stream and anaudio data bit stream, and supplies the video signal processing unitex355 with the coded video data and the audio signal processing unitex354 with the coded audio data, through the synchronous bus ex370. Thevideo signal processing unit ex355 decodes the video signal using amoving picture decoding method corresponding to the moving picturecoding method shown in each of embodiments (i.e., functions as the imagedecoding apparatus according to the aspect of the present invention),and then the display unit ex358 displays, for instance, the video andstill images included in the video file linked to the Web page via theLCD control unit ex359. Furthermore, the audio signal processing unitex354 decodes the audio signal, and the audio output unit ex357 providesthe audio.

Furthermore, similarly to the television ex300, a terminal such as thecellular phone ex114 probably have 3 types of implementationconfigurations including not only (i) a transmitting and receivingterminal including both a coding apparatus and a decoding apparatus, butalso (ii) a transmitting terminal including only a coding apparatus and(iii) a receiving terminal including only a decoding apparatus. Althoughthe digital broadcasting system ex200 receives and transmits themultiplexed data obtained by multiplexing audio data onto video data inthe description, the multiplexed data may be data obtained bymultiplexing not audio data but character data related to video ontovideo data, and may be not multiplexed data but video data itself.

As such, the moving picture coding method and the moving picturedecoding method in each of embodiments can be used in any of the devicesand systems described. Thus, the advantages described in each ofembodiments can be obtained.

Furthermore, the present invention is not limited to embodiments, andvarious modifications and revisions are possible without departing fromthe scope of the present invention.

Embodiment B

Video data can be generated by switching, as necessary, between (i) themoving picture coding method or the moving picture coding apparatusshown in each of embodiments and (ii) a moving picture coding method ora moving picture coding apparatus in conformity with a differentstandard, such as MPEG-2, MPEG-4 AVC, and VC-1.

Here, when a plurality of video data that conforms to the differentstandards is generated and is then decoded, the decoding methods need tobe selected to conform to the different standards. However, since towhich standard each of the plurality of the video data to be decodedconform cannot be detected, there is a problem that an appropriatedecoding method cannot be selected.

In order to solve the problem, multiplexed data obtained by multiplexingaudio data and others onto video data has a structure includingidentification information indicating to which standard the video dataconforms. The specific structure of the multiplexed data including thevideo data generated in the moving picture coding method and by themoving picture coding apparatus shown in each of embodiments will behereinafter described. The multiplexed data is a digital stream in theMPEG-2 Transport Stream format.

FIG. 22 illustrates a structure of the multiplexed data. As illustratedin FIG. 22, the multiplexed data can be obtained by multiplexing atleast one of a video stream, an audio stream, a presentation graphicsstream (PG), and an interactive graphics stream. The video streamrepresents primary video and secondary video of a movie, the audiostream (IG) represents a primary audio part and a secondary audio partto be mixed with the primary audio part, and the presentation graphicsstream represents subtitles of the movie. Here, the primary video isnormal video to be displayed on a screen, and the secondary video isvideo to be displayed on a smaller window in the primary video.Furthermore, the interactive graphics stream represents an interactivescreen to be generated by arranging the GUI components on a screen. Thevideo stream is coded in the moving picture coding method or by themoving picture coding apparatus shown in each of embodiments, or in amoving picture coding method or by a moving picture coding apparatus inconformity with a conventional standard, such as MPEG-2, MPEG-4 AVC, andVC-1. The audio stream is coded in accordance with a standard, such asDolby-AC-3, Dolby Digital Plus, MLP, DTS, DTS-HD, and linear PCM.

Each stream included in the multiplexed data is identified by PID. Forexample, 0x1011 is allocated to the video stream to be used for video ofa movie, 0x1100 to 0x111F are allocated to the audio streams, 0x1200 to0x121F are allocated to the presentation graphics streams, 0x1400 to0x141F are allocated to the interactive graphics streams, 0x1B00 to0x1B1F are allocated to the video streams to be used for secondary videoof the movie, and 0x1A00 to 0x1A1F are allocated to the audio streams tobe used for the secondary audio to be mixed with the primary audio.

FIG. 23 schematically illustrates how data is multiplexed. First, avideo stream ex235 composed of video frames and an audio stream ex238composed of audio frames are transformed into a stream of PES packetsex236 and a stream of PES packets ex239, and further into TS packetsex237 and TS packets ex240, respectively. Similarly, data of apresentation graphics stream ex241 and data of an interactive graphicsstream ex244 are transformed into a stream of PES packets ex242 and astream of PES packets ex245, and further into TS packets ex243 and TSpackets ex246, respectively. These TS packets are multiplexed into astream to obtain multiplexed data ex247.

FIG. 24 illustrates how a video stream is stored in a stream of PESpackets in more detail. The first bar in FIG. 24 shows a video framestream in a video stream. The second bar shows the stream of PESpackets. As indicated by arrows denoted as yy1, yy2, yy3, and yy4 inFIG. 24, the video stream is divided into pictures as I pictures, Bpictures, and P pictures each of which is a video presentation unit, andthe pictures are stored in a payload of each of the PES packets. Each ofthe PES packets has a PES header, and the PES header stores aPresentation Time-Stamp (PTS) indicating a display time of the picture,and a Decoding Time-Stamp (DTS) indicating a decoding time of thepicture.

FIG. 25 illustrates a format of TS packets to be finally written on themultiplexed data. Each of the TS packets is a 188-byte fixed lengthpacket including a 4-byte TS header having information, such as a PIDfor identifying a stream and a 184-byte TS payload for storing data. ThePES packets are divided, and stored in the TS payloads, respectively.When a BD ROM is used, each of the TS packets is given a 4-byteTP_Extra_Header, thus resulting in 192-byte source packets. The sourcepackets are written on the multiplexed data. The TP_Extra_Header storesinformation such as an Arrival_Time_Stamp (ATS). The ATS shows atransfer start time at which each of the TS packets is to be transferredto a PID filter. The source packets are arranged in the multiplexed dataas shown at the bottom of FIG. 25. The numbers incrementing from thehead of the multiplexed data are called source packet numbers (SPNs).

Each of the TS packets included in the multiplexed data includes notonly streams of audio, video, subtitles and others, but also a ProgramAssociation Table (PAT), a Program Map Table (PMT), and a Program ClockReference (PCR). The PAT shows what a PID in a PMT used in themultiplexed data indicates, and a PID of the PAT itself is registered aszero. The PMT stores PIDs of the streams of video, audio, subtitles andothers included in the multiplexed data, and attribute information ofthe streams corresponding to the PIDs. The PMT also has variousdescriptors relating to the multiplexed data. The descriptors haveinformation such as copy control information showing whether copying ofthe multiplexed data is permitted or not. The PCR stores STC timeinformation corresponding to an ATS showing when the PCR packet istransferred to a decoder, in order to achieve synchronization between anArrival Time Clock (ATC) that is a time axis of ATSs, and an System TimeClock (STC) that is a time axis of PTSs and DTSs.

FIG. 26 illustrates the data structure of the PMT in detail. A PMTheader is disposed at the top of the PMT. The PMT header describes thelength of data included in the PMT and others. A plurality ofdescriptors relating to the multiplexed data is disposed after the PMTheader. Information such as the copy control information is described inthe descriptors. After the descriptors, a plurality of pieces of streaminformation relating to the streams included in the multiplexed data isdisposed. Each piece of stream information includes stream descriptorseach describing information, such as a stream type for identifying acompression codec of a stream, a stream PID, and stream attributeinformation (such as a frame rate or an aspect ratio). The streamdescriptors are equal in number to the number of streams in themultiplexed data.

When the multiplexed data is recorded on a recording medium and others,it is recorded together with multiplexed data information files.

Each of the multiplexed data information files is management informationof the multiplexed data as shown in FIG. 27. The multiplexed datainformation files are in one to one correspondence with the multiplexeddata, and each of the files includes multiplexed data information,stream attribute information, and an entry map.

As illustrated in FIG. 27, the multiplexed data information includes asystem rate, a reproduction start time, and a reproduction end time. Thesystem rate indicates the maximum transfer rate at which a system targetdecoder to be described later transfers the multiplexed data to a PIDfilter. The intervals of the ATSs included in the multiplexed data areset to not higher than a system rate. The reproduction start timeindicates a PTS in a video frame at the head of the multiplexed data. Aninterval of one frame is added to a PTS in a video frame at the end ofthe multiplexed data, and the PTS is set to the reproduction end time.

As shown in FIG. 28, a piece of attribute information is registered inthe stream attribute information, for each PID of each stream includedin the multiplexed data. Each piece of attribute information hasdifferent information depending on whether the corresponding stream is avideo stream, an audio stream, a presentation graphics stream, or aninteractive graphics stream. Each piece of video stream attributeinformation carries information including what kind of compression codecis used for compressing the video stream, and the resolution, aspectratio and frame rate of the pieces of picture data that is included inthe video stream. Each piece of audio stream attribute informationcarries information including what kind of compression codec is used forcompressing the audio stream, how many channels are included in theaudio stream, which language the audio stream supports, and how high thesampling frequency is. The video stream attribute information and theaudio stream attribute information are used for initialization of adecoder before the player plays back the information.

In the present embodiment, the multiplexed data to be used is of astream type included in the PMT. Furthermore, when the multiplexed datais recorded on a recording medium, the video stream attributeinformation included in the multiplexed data information is used. Morespecifically, the moving picture coding method or the moving picturecoding apparatus described in each of embodiments includes a step or aunit for allocating unique information indicating video data generatedby the moving picture coding method or the moving picture codingapparatus in each of embodiments, to the stream type included in the PMTor the video stream attribute information. With the configuration, thevideo data generated by the moving picture coding method or the movingpicture coding apparatus described in each of embodiments can bedistinguished from video data that conforms to another standard.

Furthermore, FIG. 29 illustrates steps of the moving picture decodingmethod according to the present embodiment. In Step exS100, the streamtype included in the PMT or the video stream attribute informationincluded in the multiplexed data information is obtained from themultiplexed data. Next, in Step exS101, it is determined whether or notthe stream type or the video stream attribute information indicates thatthe multiplexed data is generated by the moving picture coding method orthe moving picture coding apparatus in each of embodiments. When it isdetermined that the stream type or the video stream attributeinformation indicates that the multiplexed data is generated by themoving picture coding method or the moving picture coding apparatus ineach of embodiments, in Step exS102, decoding is performed by the movingpicture decoding method in each of embodiments. Furthermore, when thestream type or the video stream attribute information indicatesconformance to the conventional standards, such as MPEG-2, MPEG-4 AVC,and VC-1, in Step exS103, decoding is performed by a moving picturedecoding method in conformity with the conventional standards.

As such, allocating a new unique value to the stream type or the videostream attribute information enables determination whether or not themoving picture decoding method or the moving picture decoding apparatusthat is described in each of embodiments can perform decoding. Even whenmultiplexed data that conforms to a different standard is input, anappropriate decoding method or apparatus can be selected. Thus, itbecomes possible to decode information without any error. Furthermore,the moving picture coding method or apparatus, or the moving picturedecoding method or apparatus in the present embodiment can be used inthe devices and systems described above.

Embodiment C

Each of the moving picture coding method, the moving picture codingapparatus, the moving picture decoding method, and the moving picturedecoding apparatus in each of embodiments is typically achieved in theform of an integrated circuit or a Large Scale Integrated (LSI) circuit.As an example of the LSI, FIG. 30 illustrates a configuration of the LSIex500 that is made into one chip. The LSI ex500 includes elements ex501,ex502, ex503, ex504, ex505, ex506, ex507, ex508, and ex509 to bedescribed below, and the elements are connected to each other through abus ex510. The power supply circuit unit ex505 is activated by supplyingeach of the elements with power when the power supply circuit unit ex505is turned on.

For example, when coding is performed, the LSI ex500 receives an AVsignal from a microphone ex117, a camera ex113, and others through an AVIO ex509 under control of a control unit ex501 including a CPU ex502, amemory controller ex503, a stream controller ex504, and a drivingfrequency control unit ex512. The received AV signal is temporarilystored in an external memory ex511, such as an SDRAM. Under control ofthe control unit ex501, the stored data is segmented into data portionsaccording to the processing amount and speed to be transmitted to asignal processing unit ex507. Then, the signal processing unit ex507codes an audio signal and/or a video signal. Here, the coding of thevideo signal is the coding described in each of embodiments.Furthermore, the signal processing unit ex507 sometimes multiplexes thecoded audio data and the coded video data, and a stream IO ex506provides the multiplexed data outside. The provided multiplexed data istransmitted to the base station ex107, or written on the recordingmedium ex215. When data sets are multiplexed, the data should betemporarily stored in the buffer ex508 so that the data sets aresynchronized with each other.

Although the memory ex511 is an element outside the LSI ex500, it may beincluded in the LSI ex500. The buffer ex508 is not limited to onebuffer, but may be composed of buffers. Furthermore, the LSI ex500 maybe made into one chip or a plurality of chips.

Furthermore, although the control unit ex501 includes the CPU ex502, thememory controller ex503, the stream controller ex504, the drivingfrequency control unit ex512, the configuration of the control unitex501 is not limited to such. For example, the signal processing unitex507 may further include a CPU. Inclusion of another CPU in the signalprocessing unit ex507 can improve the processing speed. Furthermore, asanother example, the CPU ex502 may serve as or be a part of the signalprocessing unit ex507, and, for example, may include an audio signalprocessing unit. In such a case, the control unit ex501 includes thesignal processing unit ex507 or the CPU ex502 including a part of thesignal processing unit ex507.

The name used here is LSI, but it may also be called IC, system LSI,super LSI, or ultra LSI depending on the degree of integration.

Moreover, ways to achieve integration are not limited to the LSI, and aspecial circuit or a general purpose processor and so forth can alsoachieve the integration. Field Programmable Gate Array (FPGA) that canbe programmed after manufacturing LSIs or a reconfigurable processorthat allows re-configuration of the connection or configuration of anLSI can be used for the same purpose.

In the future, with advancement in semiconductor technology, a brand-newtechnology may replace LSI. The functional blocks can be integratedusing such a technology. The possibility is that the present inventionis applied to biotechnology.

Embodiment D

When video data generated in the moving picture coding method or by themoving picture coding apparatus described in each of embodiments isdecoded, compared to when video data that conforms to a conventionalstandard, such as MPEG-2, MPEG-4 AVC, and VC-1 is decoded, theprocessing amount probably increases. Thus, the LSI ex500 needs to beset to a driving frequency higher than that of the CPU ex502 to be usedwhen video data in conformity with the conventional standard is decoded.However, when the driving frequency is set higher, there is a problemthat the power consumption increases.

In order to solve the problem, the moving picture decoding apparatus,such as the television ex300 and the LSI ex500 is configured todetermine to which standard the video data conforms, and switch betweenthe driving frequencies according to the determined standard. FIG. 31illustrates a configuration ex800 in the present embodiment. A drivingfrequency switching unit ex803 sets a driving frequency to a higherdriving frequency when video data is generated by the moving picturecoding method or the moving picture coding apparatus described in eachof embodiments. Then, the driving frequency switching unit ex803instructs a decoding processing unit ex801 that executes the movingpicture decoding method described in each of embodiments to decode thevideo data. When the video data conforms to the conventional standard,the driving frequency switching unit ex803 sets a driving frequency to alower driving frequency than that of the video data generated by themoving picture coding method or the moving picture coding apparatusdescribed in each of embodiments. Then, the driving frequency switchingunit ex803 instructs the decoding processing unit ex802 that conforms tothe conventional standard to decode the video data.

More specifically, the driving frequency switching unit ex803 includesthe CPU ex502 and the driving frequency control unit ex512 in FIG. 30.Here, each of the decoding processing unit ex801 that executes themoving picture decoding method described in each of embodiments and thedecoding processing unit ex802 that conforms to the conventionalstandard corresponds to the signal processing unit ex507 in FIG. 30. TheCPU ex502 determines to which standard the video data conforms. Then,the driving frequency control unit ex512 determines a driving frequencybased on a signal from the CPU ex502. Furthermore, the signal processingunit ex507 decodes the video data based on the signal from the CPUex502. For example, the identification information described inEmbodiment B is probably used for identifying the video data. Theidentification information is not limited to the one described inEmbodiment B but may be any information as long as the informationindicates to which standard the video data conforms. For example, whenwhich standard video data conforms to can be determined based on anexternal signal for determining that the video data is used for atelevision or a disk, etc., the determination may be made based on suchan external signal. Furthermore, the CPU ex502 selects a drivingfrequency based on, for example, a look-up table in which the standardsof the video data are associated with the driving frequencies as shownin FIG. 33. The driving frequency can be selected by storing the look-uptable in the buffer ex508 and in an internal memory of an LSI, and withreference to the look-up table by the CPU ex502.

FIG. 32 illustrates steps for executing a method in the presentembodiment. First, in Step exS200, the signal processing unit ex507obtains identification information from the multiplexed data. Next, inStep exS201, the CPU ex502 determines whether or not the video data isgenerated by the coding method and the coding apparatus described ineach of embodiments, based on the identification information. When thevideo data is generated by the moving picture coding method and themoving picture coding apparatus described in each of embodiments, inStep exS202, the CPU ex502 transmits a signal for setting the drivingfrequency to a higher driving frequency to the driving frequency controlunit ex512. Then, the driving frequency control unit ex512 sets thedriving frequency to the higher driving frequency. On the other hand,when the identification information indicates that the video dataconforms to the conventional standard, such as MPEG-2, MPEG-4 AVC, andVC-1, in Step exS203, the CPU ex502 transmits a signal for setting thedriving frequency to a lower driving frequency to the driving frequencycontrol unit ex512. Then, the driving frequency control unit ex512 setsthe driving frequency to the lower driving frequency than that in thecase where the video data is generated by the moving picture codingmethod and the moving picture coding apparatus described in each ofembodiment.

Furthermore, along with the switching of the driving frequencies, thepower conservation effect can be improved by changing the voltage to beapplied to the LSI ex500 or an apparatus including the LSI ex500. Forexample, when the driving frequency is set lower, the voltage to beapplied to the LSI ex500 or the apparatus including the LSI ex500 isprobably set to a voltage lower than that in the case where the drivingfrequency is set higher.

Furthermore, when the processing amount for decoding is larger, thedriving frequency may be set higher, and when the processing amount fordecoding is smaller, the driving frequency may be set lower as themethod for setting the driving frequency. Thus, the setting method isnot limited to the ones described above. For example, when theprocessing amount for decoding video data in conformity with MPEG-4 AVCis larger than the processing amount for decoding video data generatedby the moving picture coding method and the moving picture codingapparatus described in each of embodiments, the driving frequency isprobably set in reverse order to the setting described above.

Furthermore, the method for setting the driving frequency is not limitedto the method for setting the driving frequency lower. For example, whenthe identification information indicates that the video data isgenerated by the moving picture coding method and the moving picturecoding apparatus described in each of embodiments, the voltage to beapplied to the LSI ex500 or the apparatus including the LSI ex500 isprobably set higher. When the identification information indicates thatthe video data conforms to the conventional standard, such as MPEG-2,MPEG-4 AVC, and VC-1, the voltage to be applied to the LSI ex500 or theapparatus including the LSI ex500 is probably set lower. As anotherexample, when the identification information indicates that the videodata is generated by the moving picture coding method and the movingpicture coding apparatus described in each of embodiments, the drivingof the CPU ex502 does not probably have to be suspended. When theidentification information indicates that the video data conforms to theconventional standard, such as MPEG-2, MPEG-4 AVC, and VC-1, the drivingof the CPU ex502 is probably suspended at a given time because the CPUex502 has extra processing capacity. Even when the identificationinformation indicates that the video data is generated by the movingpicture coding method and the moving picture coding apparatus describedin each of embodiments, in the case where the CPU ex502 has extraprocessing capacity, the driving of the CPU ex502 is probably suspendedat a given time. In such a case, the suspending time is probably setshorter than that in the case where when the identification informationindicates that the video data conforms to the conventional standard,such as MPEG-2, MPEG-4 AVC, and VC-1.

Accordingly, the power conservation effect can be improved by switchingbetween the driving frequencies in accordance with the standard to whichthe video data conforms. Furthermore, when the LSI ex500 or theapparatus including the LSI ex500 is driven using a battery, the batterylife can be extended with the power conservation effect.

Embodiment E

There are cases where a plurality of video data that conforms todifferent standards, is provided to the devices and systems, such as atelevision and a cellular phone. In order to enable decoding theplurality of video data that conforms to the different standards, thesignal processing unit ex507 of the LSI ex500 needs to conform to thedifferent standards. However, the problems of increase in the scale ofthe circuit of the LSI ex500 and increase in the cost arise with theindividual use of the signal processing units ex507 that conform to therespective standards.

In order to solve the problem, what is conceived is a configuration inwhich the decoding processing unit for implementing the moving picturedecoding method described in each of embodiments and the decodingprocessing unit that conforms to the conventional standard, such asMPEG-2, MPEG-4 AVC, and VC-1 are partly shared. Ex900 in FIG. 34A showsan example of the configuration. For example, the moving picturedecoding method described in each of embodiments and the moving picturedecoding method that conforms to MPEG-4 AVC have, partly in common, thedetails of processing, such as entropy coding, inverse quantization,deblocking filtering, and motion compensated prediction. The details ofprocessing to be shared probably include use of a decoding processingunit ex902 that conforms to MPEG-4 AVC. In contrast, a dedicateddecoding processing unit ex901 is probably used for other processingunique to an aspect of the present invention. Since the aspect of thepresent invention is characterized by inverse quantization inparticular, for example, the dedicated decoding processing unit ex901 isused for inverse quantization. Otherwise, the decoding processing unitis probably shared for one of the entropy decoding, deblockingfiltering, and motion compensation, or all of the processing. Thedecoding processing unit for implementing the moving picture decodingmethod described in each of embodiments may be shared for the processingto be shared, and a dedicated decoding processing unit may be used forprocessing unique to that of MPEG-4 AVC.

Furthermore, ex1000 in FIG. 34B shows another example in that processingis partly shared. This example uses a configuration including adedicated decoding processing unit ex1001 that supports the processingunique to an aspect of the present invention, a dedicated decodingprocessing unit ex1002 that supports the processing unique to anotherconventional standard, and a decoding processing unit ex1003 thatsupports processing to be shared between the moving picture decodingmethod according to the aspect of the present invention and theconventional moving picture decoding method. Here, the dedicateddecoding processing units ex1001 and ex1002 are not necessarilyspecialized for the processing according to the aspect of the presentinvention and the processing of the conventional standard, respectively,and may be the ones capable of implementing general processing.Furthermore, the configuration of the present embodiment can beimplemented by the LSI ex500.

As such, reducing the scale of the circuit of an LSI and reducing thecost are possible by sharing the decoding processing unit for theprocessing to be shared between the moving picture decoding methodaccording to the aspect of the present invention and the moving picturedecoding method in conformity with the conventional standard.

In summary, the present invention provides an improved video encodingand decoding method, which maintains the advantages of LCU-based filterparameter signaling as compared to frame-based filter parametersignaling, but considerably reduces signaling overhead. Therefore,signaling syntax is modified by grouping LCUs (Largest Coding Units)together for signaling employing a mapping function. Consequently,filter parameters no longer need to be signaled for each single LCU, butfor a group of several LCUs. The syntax structure of the inventionavoids redundancies present in the state of the art as far as possibleand thus increases the information content of the syntax elements. Atthe decoder side, the mapping function is applied to infer informationabout the filter parameters to be applied to a current LCU frominformation encoded in different syntax structures.

1. A decoding method for decoding a picture from a bitstream on thebasis of Largest Coding Units, the decoding method comprising: obtaininggroup information specifying the number of groups in the picture, eachof the groups including one or more Largest Coding Units, by parsing afirst syntax structure of the bitstream; obtaining unit informationspecifying the number of the Largest Coding Units in the picture, byparsing a second syntax structure of the bitstream; and deriving filterparameters for a current group to be applied in decoding a currentLargest Coding Unit in the current group using the group information andthe unit information.
 2. The method according to claim 1, wherein saidfilter parameters are for at least one filter comprising a SampleAdaptive Offset and/or an Adaptive Loop Filter.
 3. The method accordingto claim 1, further comprising: obtaining reference informationreferencing to said first and said second syntax structure, by parsing athird syntax structure.
 4. The method according to claim 1, wherein thegroup information includes group width information specifying the numberof the groups in a width direction of the picture and group heightinformation specifying the number of the groups in a height direction ofthe picture.
 5. The method according to claim 1, wherein the unitinformation includes unit width information specifying the number ofLargest Coding Units in a width direction of the picture and unit heightinformation specifying the number of Largest Coding Units in a heightdirection of the picture.
 6. The method according to claim 5, whereinthe unit information includes information specifying the height and thewidth of the picture and information specifying the height and the widthof a Largest Coding Unit.
 7. The method according to claim 1, whereinthe filter parameters are derived by applying the group information andthe unit information to a predetermined mapping function.
 8. The methodaccording to claim 1, wherein the bitstream includes functioninformation specifying the mapping function.
 9. An encoding methodemploying variable filter parameters for encoding a picture on the basisof Largest Coding Units into a bitstream, wherein the filter parametersare determined and encoded adaptively on the basis of groups of pluralLargest Coding Units, the encoding method comprising: generating syntaxelements specifying the number of said groups in the picture; andincluding said syntax elements into a syntax structure adapted fordefining filter parameters on the basis of single Largest Coding Unitsin place of syntax elements specifying the number of Largest CodingUnits in the picture.
 10. The method according to claim 9, wherein saidfilter parameters are for at least one filter comprising a SampleAdaptive Offset and/or an Adaptive Loop Filter.
 11. The method accordingto claim 9, wherein said syntax elements comprise a syntax elementspecifying the number of Largest Coding Unit groups in the direction ofpicture width and a syntax element specifying the number of LargestCoding Unit groups in the direction of picture height.
 12. The methodaccording to claim 9, wherein said generating generates the syntaxelements specifying the number of said groups in the picture based onsaid syntax elements specifying the number of Largest Coding Units inthe picture and additional parameters specifying the number of LargestCoding Units that are grouped together.
 13. The method according toclaim 12, wherein said additional parameters comprising a parameterindicating the number of Largest Coding Units that are grouped togetherin the direction of picture width and a parameter indicating the numberof Largest Coding Units that are grouped together in the direction ofpicture height.
 14. The method according to claim 9, wherein said numberof groups in the picture is determined based on a rate-distortionmeasure.
 15. The method according to claim 9, further including applyinga predetermined mapping function on said syntax elements specifying thenumber of Largest Coding Unit groups in the picture and additionalparameters specifying the number of Largest Coding Units in the picture,in order to determine for each Largest Coding Unit, to which LargestCoding Unit group it belongs, thereby determining the filter parametersto be applied to each particular Largest Coding Unit.
 16. The methodaccording to claim 15, wherein information specifying said mappingfunction is included in the encoded bitstream.
 17. A decoding apparatusfor decoding a picture from a bitstream on the basis of Largest CodingUnits, the decoding apparatus comprising: a first parser for parsing afirst syntax structure of the bitstream to obtain group informationspecifying the number of groups in the picture, each of the groupsincluding one or more Largest Coding Units; a second parser for parsinga second syntax structure of the bitstream to obtain unit informationspecifying the number of the Largest Coding Units in the picture; and afilter information deriving unit for deriving filter parameters for acurrent group to be applied in decoding a current Largest Coding Unit inthe current group using the group information and the unit information.18. An encoding apparatus employing variable filter parameters forencoding a picture on the basis of Largest Coding Units into abitstream, wherein the filter parameters are determined and encodedadaptively on the basis of groups of plural Largest Coding Units, theencoding apparatus comprising: a unit for generating syntax elementsspecifying the number of said groups in the picture; and a unit forincluding said syntax elements into a syntax structure adapted fordefining filter parameters on the basis of single Largest Coding Unitsin place of syntax elements specifying the number of Largest CodingUnits in the picture.
 19. A decoding apparatus for decoding a picturefrom a bitstream on the basis of Largest Coding Units, the decodingapparatus comprising: one or more processors; and storage coupled to theone or more processors, wherein the one or more processors areconfigured to perform operations for obtaining group informationspecifying the number of groups in the picture, each of the groupsincluding one or more Largest Coding Units, by parsing a first syntaxstructure of the bitstream; obtaining unit information specifying thenumber of the Largest Coding Units in the picture, by parsing a secondsyntax structure of the bitstream; and deriving filter parameters for acurrent group to be applied in decoding a current Largest Coding Unit inthe current group using the group information and the unit information.20. An encoding apparatus employing variable filter parameters forencoding a picture into a bitstream on the basis of Largest codingUnits, wherein the filter parameters are determined and encodedadaptively on the basis of groups of plural Largest Coding Units, theencoding apparatus comprising: one or more processors; and storagecoupled to the one or more processors, wherein the one or moreprocessors are configured to perform operations for generating syntaxelements specifying the number of said groups in the picture, andincluding said syntax elements into a syntax structure adapted fordefining filter parameters on the basis of single Largest Coding Unitsin place of syntax elements specifying the number of Largest CodingUnits in the picture.